Custom appointment availability with Google Calendar integration

I’m wanting to offer Appointment scheduling to my customers for 2 hour blocks of time. I have set this up in my “Appointments” section on Keap, however, customers now have the option to schedule their 2 hour appointment at 15 minute availabilities…
This is a problem because if I am opening up my calendar from 8-6, and a customer schedules their appointment at 9:15, I lose an effective appointment slot.
Keap has informed me that they don’t have a way to only open scheduling windows right now but they are aware of the need…
Does anyone have a plausible workaround?