How to set up 30min and 50min sessions

First I have a padding of 15 min set for after each service appt. I need 15 min. to set up for the next appointment and why I activated padding, which I hope is right.

I don't wish to set up any service providers and need the ability to set up appts. for 30 min and 50 min sessions. I don't want them to overlap of course and still have the padding factor in.

Example:
Open 8am to 5pm
6 Services are available
Services are for 1 customer only
Sessions avail - 30 or 50 min

1 customer books 30 min at 8am and at 8:30am padding of 15 min kicks in
Next appt available 8:45am
1 customer books 50 min at 8:45am and at 9:35am padding of 15 min kicks in
Next appt available at 9:50am

How exactly would I accomplish this? Thanks!