I went to this year's interview weekend for UCLA, and it was February 4th-6th. All of the other interview invites that I received were also for the same weekend, except for the University of Kentucky, which was the last weekend in January.
I went to UW for undergrad, and from what I saw, the clinical psych interview weekend was usually in late February. I'm not 100% sure on that one though, because I didn't apply to UW for grad school.
It seemed to me like early February was definitely the most popular interview time. Early January seemed a lot less popular, so I think you would be safer to travel then. I hope this helps a little!