How do I add padding to my time slots?

I realize this question has been asked many times, and I've reviewed the prior questions, but I need someone to guide me through my particular situation as I'm still a bit unclear on the specifics.

I need to offer two services, one is for 55 minutes and one is for 85 minutes. Each would need a 5 minute pad at the end so that I can gather myself and take some notes before the next appointment (meaning that the 60 minute or 90 minute blocks are being reserved, depending on the service). I would like the client to see that they are booking a 55 or 85 minute appointment (and ideally, the appointment when sent to their Google Calendar would also show up as 55 or 85 minutes) but have A+ block off 60 or 90 minutes, as appropriate.

What should I set for my base time, what should I set for my service duration and what code should I add to my functions.php of my current theme?