Booking an appoointment within 24 hours

Hi there is an issue with booking an appointment within 24 hours of it taking place.
Tested booking an appointment and was not able to select it. is it possible to change the settings so that a user can book an appointment up to 30 mins before it takes place?

Plugins:
Appointment +
Marketpress

website: http://tinyurl.com/lguqz6p
support access open

Thanks

Tom