When a visitor opens your booking chat and sees a list of times, those times come from rules you set once and rarely look at again: your opening hours, how long a booking lasts, how much notice you need and how the booking connects to your own calendar. Get these wrong and visitors book times you cannot honour, or see no times at all. This guide explains the availability rules behind online booking, how to choose sensible values for different kinds of business, how calendar feeds and sync work, and the mistakes that cause trouble.
Different booking products offer different levels of control. Where we describe Crescelo, we describe what it does today. Some features in this article, such as per-service durations, buffers and staff calendars, are things fuller scheduling systems do; Crescelo's built-in picker keeps to opening hours and one slot length, and you can use Calendly or Cal.com links for more complex scheduling.
The building blocks of availability
| Rule | What it decides | Typical mistake |
|---|---|---|
| Opening hours | Which days and hours can be booked | Leaving lunch breaks or closed days open |
| Slot length | How long each bookable time lasts | Choosing a length shorter than the real service |
| Lead time | How soon before a slot it can be booked | Allowing bookings 10 minutes ahead when you need a day |
| Booking window | How far ahead people can book | Opening a year of slots you cannot promise |
| Breaks and closures | Lunch, holidays, training days | Forgetting a bank holiday |
| Capacity | How many bookings can overlap | Assuming one when you have two staff, or the reverse |
| Time zone | How times are shown and stored | Mixing your zone with the visitor's |
Each of these can be simple or sophisticated. The right level depends on your business, and more sophistication is not always better.
Choosing your opening hours for booking
Booking hours are not always your public opening hours. You might accept bookings from 9 to 5 but only take walk-ins outside them, or you might close bookings an hour before closing so the last customer is not rushed. Set booking hours to what you can genuinely serve.
- Include the days you are open and no others.
- Exclude lunch or admin time if you cannot serve clients then.
- Leave a buffer at the end of the day.
- Update them for seasonal changes and holidays.
If your product supports only weekly hours and not one-off closures, remember to adjust your hours before a holiday or use another mechanism to close specific dates.
Choosing a slot length
The slot length is the block of time each booking occupies. It should match what the service actually takes, including the time before and after that you need.
| Business | Common approach |
|---|---|
| Barbershop with mostly one service | A single slot length such as 30 minutes |
| Clinic with standard consultations | A fixed slot such as 30 or 45 minutes |
| Coach or consultant | One slot length per call type, using separate booking links if you offer several |
| Salon with many services of different lengths | A scheduling tool with per-service durations, or separate booking links for long and short services |
| Studio classes | A fixed schedule with capacity |
Crescelo's built-in picker uses one slot length, such as 30, 45 or 60 minutes, per assistant. If your services have very different lengths, either choose the length of your most common service and describe longer services in the chat so the visitor books consecutive slots or contacts you, or use Calendly or Cal.com links for the services that need their own durations.
Lead time and booking window
- Lead time: how much notice you need. A same-day salon may accept bookings an hour ahead; a clinic may need a day; a consultant may need a week.
- Booking window: how far ahead you accept bookings. Most small businesses open four to eight weeks.
Short lead times increase bookings but raise the risk of late arrivals and last-minute changes. Long windows reduce your flexibility. Review both every few months.
How slot locking prevents double bookings
Availability is only trustworthy if two people cannot book the same slot. A good system checks availability again at the moment of confirmation and locks the slot while the booking is saved, so the second person is offered the next time instead. Crescelo's built-in picker hides slots that are already taken and locks a slot while it is being booked. The mechanics are explained in how online booking avoids double bookings.
Your own calendar and the calendar feed
You will want bookings to appear in the calendar you already live in. There are two common approaches, and it matters which one you have.
| Approach | What it does | Consequence |
|---|---|---|
| One-way feed (read-only) | Bookings are published as a feed that Google, Apple or Outlook Calendar subscribes to | Bookings show in your calendar, but events you add there do not change the booking slots |
| Two-way sync | The booking system reads your calendar's busy times and writes bookings back | Personal events block slots automatically |
Crescelo provides the one-way feed today: copy the private feed address from the Appointments page and subscribe in Google Calendar (Other calendars, then From URL), Outlook or Apple Calendar. Two-way sync is on the roadmap but not available yet. That has a practical consequence: if you add a personal appointment in your own calendar, the assistant will still offer that time. To keep the two consistent, reduce your booking hours to times you are genuinely free, or block the time using the opening hours settings.
Calendly and Cal.com links, which Crescelo supports, offer their own calendar connections if you need two-way behaviour. See seeing AI bookings in Google and Outlook Calendar.
Time zones
Store times in a standard form and display them in the visitor's zone, stating the zone in the confirmation. Watch for daylight saving changes: a booking made for 9 a.m. should stay at 9 a.m. local time on the day, even if clocks change in between. If you serve visitors in other zones, say so in the chat and in the confirmation, for example '2:30 p.m. Eastern Time (7:30 p.m. UK time)'.
Example setups
A single-chair barbershop
Hours Tuesday to Saturday 9 to 6, slot length 30 minutes, lead time one hour, window four weeks. Longer services, such as a cut and beard, are described in the knowledge base as two consecutive slots.
A physiotherapy clinic
Hours Monday to Friday 8 to 5, slot length 45 minutes for a standard session, lead time one day, window six weeks. Initial assessments use a separate booking link with a longer duration through a scheduling tool.
A solo consultant
Hours chosen around deep-work time, slot length 30 minutes for introductory calls, lead time two days, window three weeks, with a clear time zone in every confirmation.
Testing your rules
- Open the booking in a private window and look at the first available slot. Is it sooner than you can honour?
- Check the last slot of the day. Does it leave you enough time?
- Check a day you are closed and a holiday.
- Book a slot, then try to book the same slot from another window.
- Look at the confirmation and calendar feed entry.
- Try a booking from another time zone if you serve one.
Retest whenever you change hours, add services or change your team.
Common mistakes
- Slot lengths shorter than the service.
- No lead time, so people book while you are already on your way home.
- Forgetting to close for holidays.
- Assuming personal calendar events block bookings when they do not.
- Opening too long a window and then rearranging.
- Not stating the time zone.
- Not testing after changes.
Related reading
- AI appointment booking explains what a trustworthy booking system must do end to end.
- Seeing AI bookings in Google and Outlook Calendar covers feeds, refresh delays and clashes.
- How to reduce no-shows shows what to send after a booking is made.
- Frictionless self-serve rescheduling keeps changes from becoming cancellations.
A short review routine
Availability rules drift as your business changes. Once a quarter, open your booking settings and check that hours match your real week, that the slot length still fits your main service, that holidays are covered and that the lead time still works. Book a test appointment and follow it through to the confirmation and the calendar feed. Ten minutes a quarter prevents most availability problems.
Frequently asked questions
How do I set availability for online booking?
Set your booking days and hours, the slot length, lead time and booking window, and connect the booking to your calendar through a feed or sync.
What slot length should I choose?
Choose the length of your most common service including any time before and after. Use separate booking links or a scheduling tool for services with very different lengths.
Does the booking block my personal calendar events?
Only with two-way sync. Crescelo provides a one-way, read-only feed today, so events you add in your own calendar do not block slots yet.
How do I see bookings in Google Calendar?
Copy the calendar feed address from the Appointments page and subscribe to it in Google Calendar under Other calendars, From URL.
How do I stop double bookings?
Use a booking system that locks a slot while it is being booked and hides slots that are taken.
What is lead time?
The minimum notice before a slot that a booking is accepted, for example a day.
See how it works in the appointment booking feature, read AI appointment booking and start a free trial.
Further reading
- Google Calendar API overview: How calendar events are read and written by software.
- Google Search Central: creating helpful, people-first content: What Google looks for in useful pages.
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