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How long is not long?

He may still be a nervous about coming out although if he lets you pick him up & stroke him it does sound as though he's settling in well.
When you say grumpy during the day when is he getting up other than 1am that is?
Most russians, or at least the ones I've had seem to be early risers in the evening but then prefer to do their own thing more with less interaction later in the evening or late at night.
It may well be worth trying to coax him out earlier, do it gradually & make it worth his while, give him some of his food or a treat or two if he does come out when you try to wake him, just make some gentle noises in the cage & see if he'll come out of his own accord rather than taking him out of his house or anything too scary.
What's his set up like? Does he have places to hide away around the cage if he gets a bit nervous?