Absolutely right, some clients (but only some, luckily) most definitely like to faff about in their own house.... but I think this is one of the benefits to the client of having their tan in their own home... A few weeks ago a new client announced "I'm just going to walk the dog" while I was setting up!!!
One thing I always strive for, and that's to ensure the client feels they're getting their money's worth so I'd never want them to feel I'm hurrying them along. If I think I'm going to be tight on time, when taking the booking I'll always say "I can certainly do that time, as long as I can get to xxx by 7.30pm that should be absolutely fine" or something similar.
First-time clients require more time to allow for the consultation, then you'll be able to gauge how long you'll need for your regulars. I always allow 40 minutes for new single-appointment clients, less for regular single clients, but most of my appointments are for at least 2+ clients and I allow at least 10 minutes extra for each person.
You'll then have to work out how long it'll take to travel between clients' homes.
It'll all become apparent the more you do, good luck xx