Yes that is 2-3 weeks for our adult.

Somewhere we read not to overfeed them and that they are indeed not used to a lot of food and they get fat or store fat easily and possibly end up with fatty liver disease and shortens life span.

Don't know where we read it, but it's seemed to be ok for us so far.

Don't worry too much, we debate on when the last time ours ate. Usually it is decided when we end up with a large rat that no one wants.