I'm not as quick to dismiss the worry as Hili, I think it might mean everything is fine and it might be a problem. 3 hours a day of almost everything can be considered an addiction. I think the best thing to do is to talk to him about it. It might be that he found a cool new hobby and it might be that he's getting more and more drawn into it.
There are 2 things to worry about - the first is the addiction factor of this, the second is the money aspect of it. Are big sums of money involved in this? is he down sizing on other expenses to put into poker? does this activity come instead other activities or chores or other things he's supposed to do? is this becoming a big thing in his life? does he only make friends who are into the same hobby?
I don't know your level of involvement with him - do you have a joined bank account? do you live together? if so, then I think it's only fair to set a limit to the money that goes into his new hobby (just like other couple might have about their hobbies).
I think the answer to the question of whether you should worry about or not should be worried or not should be based on your instincts, and is bigger then just 3 hours of poker and more about his overall behavior and approach.
