Simples. I'm wondering why you're even bothering to ask.
The tradesman is supplying their labour & equipment. Just ask them how long it will take to do the job, then make that length of time a part of the contract.
Do a bit of easy math & work out how much they pay themselve's. If it's £100 a day then they're amateurs. If it's £1000 a day, then they really should consider a career in law.