I have just checked your OS Services Booking system, i found some problems on your setting
1. You don't have any employees, in OS Services Booking, employees are very important. You should create at least one default employee and assign him to your services to see the timeslots to be shown.
2. Your Working time setting up are wrongly also, the working time should be within a day, and end time must later than start time. In your setting, the start time is 9:00 AM and end time is 4:00 AM -> wrongly.
Please correct your setting to make OS Services Booking to be shown properly.