in appointments+ scheduling appointments of different lengths consecutively

I need to be able to schedule a 15 min appointment and a 90 min appointment consecutively. someone schedules a 15 min brow wax for 9 am and then someone is able to schedule a 90 min massage at 9:15. but the 90 min service is showing up as available in 90 min intervals only... 9 am, 10:30 am, etc. this means my practitioner is sitting around doing nothing from 9:15 to 10:30..