The builders/developers would want a set price.
So pricing per day or per hour is of no use to them. You will need to charge per unit (overall total)
Charge well, probably 4-6 times as much as a general one off clean.
They will probably go for the cheapest quote anyway - BUT as you say it needs to be worth your while as you going to absolutely hate the job, and hate the entire day! Its a right ball ache.
Remember get a scratch damage waiver for the windows and anything else, like the baths, mirrors signed before you even go on site. They are very likely to have been scratched when installing or general work inside and they haven;t been covered up or look after - and they will look to claim that from you.