Don't worry about about asking questions- many more people will find them and the replies interesting than actually post a reply. Keep 'em coming!
There are good reasons why the advice is often to put them out after 24 hours if the mothering up process is complete - largely around infection control. However, if the lambs go out into wet cold weather and they succumb to hypothermia, you haven't gained much. In your situation, with single use pens, then I would say your peace of mind is everything. Presumably you are still feeding the ewes, so if you do that twice a day, you can still check on the lambs too. The ewes will appreciate the exercise and a nibble at some grass if you have any after a week confined to a pen as well.
So I think up to a week is fine, but if one more day brings sunshine, then that's also fine. But once they are outside, be prepared to waste lots of time just watching the lambs larking about.