Cats can hold it for a few days when stressed. Your kitty is probably still adjusting to their new home. I wouldn't worry about it yet. If, say, 3 days pass and nothing happens - then, I'd worry. But, the first 48 hours are such a huge adjustment period.
Also (not to worry you) make sure the kitty isn't peeing elsewhere. Sometimes, in a new place, they hide where they're going.
First special delivery - April 2010 :