I'm in Miami and my GMT setting is configured as such (GMT - 4). Yet when I log into the booking system, the date at the top right-hand corner is one day ahead of the actual date (i.e. today is the 14th, it shows today as the 15th). So I would imagine that if I try to make a reservation, that time wouldn't be correct as well.
Welcome dslin001. This first iteration of the booking system does have some quirks around timezones and dates; the revised one will be much better. However given that your timezone is set correctly you should still be able to make a booking and have your session start at the time you expect. To check this, make a booking for some convenient time and give it a try