I'm booking people for 60 minute sessions and they can only book on the hour..

I am a massage therapist offering 60 minute sessions as an option. As it is set up now, my clients can only book on the hour so if someone wants to come for 12:30pm they can't they either have to pick 1pm or 12pm. This is a potential loss of bookings. I need to offer at least bookings every 30 mins of the hours I am open. Can you assist me please?
Dru