You have a couple of options here connection wise. You can charge for it and get an electrician in to do the final connection or you can get the customer to do it (if it's that sort of household and Mr Customer is able - you'll usually find the type of customer to have electric underfloor heating is normally a bit of a keen DIYer or just has the wedge to pay you to do it).
If the customer does it, which they can, they have to get their local council to check it before using it, in which case most don't and just approve it after a few questions, and when they do to be honest they're the council and haven't got a clue what they're looking at anyway so after another continuity test it's approved.
Charge a decent day rate but call it a total price so WHEN you finish early the customer isn't asking for some knocked off the bill.
I used to go in o day one and prep the floor, fit the insualion, lay the cable and pour the self-levelling compound down and then go home at lunch time and then go on day two and tile / grout. That's for a floor of anything beteen 6 and 15 meters and I used to charge a weeks work.... and get every job. And many of them.
