what is the recommened time to let concrete for a basement set before putting the house on top?

Answer 1

That will depend in part on the type of concrete and the weather. Usually you want to wait a few days but there are mixes that can be poured and built on the same day.

Answer 2

The house is probably going to go up kind of slowly. Unless you're dropping in a prefab on it, you can start construction within a couple of days. As long as the concrete isn't "green". You're going to add the mass on slowly as you build it.