multimaster

G'day I've got a young (about 3 weeks) budgie and I'm wondering when I can start taking him from the nest for decent periods of time. At the moment, I've been taking him out for a couple minutes and then putting him back in and mum doesn't seem to mind too much but I don't want to risk having to hand feed him if I can avoid it. I've started putting millet sprays in the box in the hopes that he may start eating by himself before leaving the box. If I take him out for 10 or 15 minutes, is mum likely to reject him or anything? How long can I take him out for and when can I move him into his own cage. Thanks for any advice James