When you set up your business, you pick a single time zone. Every booking your business takes is anchored to that zone. A 2:00 PM appointment is always 2:00 PM in your business's zone, no matter where the client is when they book it.
This is the simplest model for a solo practice. Your hours, your availability, your calendar, and your reminders all run on your time.
What the client sees
A client opening your booking page from a different time zone sees the appointment time in their zone, with a small note like "(Pacific Time)" so they know your local time too. When they confirm, the booking is stored as your local wall-clock time. The reminder they get the day before shows the same translation again.
This protects against the most common mix-up: a client in New York thinking "3:00 PM" is 3:00 PM Eastern when you, in San Diego, meant 3:00 PM Pacific.
When you travel
Traveling does not change your business's time zone. If you fly to a conference for a week, your booking page keeps showing your home schedule and your home hours. This is usually what you want; you do not want clients seeing a different schedule depending on where you happen to be standing.
If you are permanently moving your practice to a new city, change the time zone in Settings, Business. Existing bookings are not retimed; they stay on the wall-clock moment they were created at.
Daylight saving time
ApptOnly handles DST automatically. When the clock springs forward in March or falls back in November, your hours shift with it. A client booking at 10:00 AM on a Monday in February and a client booking at 10:00 AM on a Monday in April both see 10:00 AM your time, even though those are different UTC moments.
The one edge case is a booking that lands inside the missing or doubled hour on the day of the change itself. Practitioners in the US can avoid the spring-forward gap by not booking 2:00 to 3:00 AM appointments, which most of us are not doing anyway.
Why this matters when looking at reports
Numbers in your dashboard (revenue by day, bookings per week, etc.) are computed in your business time zone, not UTC and not the client's zone. If you see a number that seems off, double-check that the period you are looking at matches what you mentally drew on the calendar.