hello i asked the following question before 
"1. i have a problem i want my customer to book 15 min appointment with 5 minute buffer time. for example if someone book an appointment from 9:00 am to 9:15 am and it gets booked then the next customer should see time slots starting from 9:20 am to 9:35 am with 5 min gap automatically. but if i set block time to 5 min it books 2 slots instead of 5 minute gap. please help me with a solution" to which you replied to set slot step to 5 but if i do that then the time slots are 5 minute each booking 3 at once while i want each time slot to be of 15 minute and once a time slot is book a single one then 5 minute buffer is added to the the slot suppose if 9-1:15 is booked the next slot starts from 9:20-9:35 instead of 9:15-9:30 
making slot step to be 5 doesn't solve it it makes it more complicated