When booking an appointment in MassageBook Mobile, times that initially show as available for selection are based on the hours added to the Availability section of your Business Profile in the desktop version.
If you select Show 24 Hours next to the selected date on the Schedule, you're given the option to select between 12am - 11pm. This allows you to book at anytime during the day and outside of your normal availability.
When booking on the Schedule, you are not limited to your availability hours and have complete control over booking times. You'll be warned about booking during an unavailable time and will have the option to override it if you choose.
When booking online, Clients can only choose start times within your availability hours that don't conflict with any other appointments or Blocked Time.