Wait until contract is exchanged and then there will be a completion date set (or on notice if its a new build). It usually complete on a Friday, so people can move in on the weekend. The whole thing (if no hiccups) can be from 6 to 8 weeks. Thou sometimes you'll see in Law journals on some practices saying they've done it in like 48 hours or something, but it's usually where the searches are already done when the last buyer dropped out like the week before on a new build thats completed with no chain.
so short answer - give it about 8 weeks.