[Relax? The entire day? That isn't what Sebastian is supposed to do. It isn't what he wants to do, for that matter (not that anyone should care about Sebastian's feelings regarding anything).
After seeing to Ciel and Madam Red's needs (and shooing away some service bots trying to steal Sebastian's job) Sebastian does dutifully start investigating the new prison for a way out, like he should, but then he notices... ah, those are muddy footprints leading up to the cabin the young master and his aunt have been assigned. Sebastian might as well take care of it; he'll be quicker and do it better than any of the automata, he's sure. He walks up to one of the cleaning bots, announces that he will just be borrowing its mop for a minute, please excuse him...]
That one non-bot cleaning your floors and serving your food
[It just kind of escalates after that, okay? Throughout the next two days you might find one human(?) working alongside the service bots: cleaning the floors, approaching you with a tray and a smile politely asking if you'd like a drink, or waiting behind a counter or a stall asking what food you would like to order. Or serving you drugs. Hey, you do you - what does he care? ¯\_(ツ)_/¯
(The bots gave up hours ago trying to get Sebastian to sit down and let himself be pampered. They have a new co-worker now.)]
Revenge and other drugs
[Unfortunately for Ciel, a butler's duties include making sure his master doesn't waste his time on frivolities and that he learns what he must. Sebastian also enjoys the tutor role. If anyone passes by the Picnic Park Pavilion they might hear pieces of today's important and appropriate-for-a-thirteen-year-old lecture:]
...now, opium. You see how it differs slightly from the others? The lethal amount for a grown man of, say, my size would be...