Scheduler booking page week view fetching the time format from the system/browser time settings. These settings can also vary depending on the preferred language.
If the booking page is loaded in a browser/system with a default time format of 24hr clock, it will also show the time slots in 24hr clock format. Similarly, if the browser has a default time format with 12hr clock, it will show the slots in 12hr format.
There is no way to change these settings except for writing a code to override these settings in the App that loads the scheduler.