A lot of the answer to this question depends upon the babies and the mom. I had to wean one set of babies away at 5 weeks of age because mom was wanting to breed and mounting them and attacking them. However, this is very unusual. I've had other moms that pitched a fit when I weaned away the bucks at 7.5 weeks of age and were happy they could still keep the girls with them for a bit longer.
I think what you need to consider is the needs of the baby and the mom. Do they get along well together? Then leave them together for 7 weeks or so and let them have that time together before baby is put into the stressful environment of a new home, etc.
As a breeder, I almost never let a baby leave here unless it has succesfully lived away from mama for a minimum of one week. I want to watch the baby and make sure it has a good adjustment living away from mama. Of course, it is usually in a cage with its littermates...but still yet - for a week it is on solids without mama and I get to make sure it does ok.
I hope this helps. While it is possible to wean early - I try to NOT do so if I can help it.
Peg