Well, I flew cross-county not even six weeks after my 1st TKR, but it was a family emergency. The ice at destination scared me, and my surgeon wasn't happy to hear about the flying, but I lived.
I took a real vacation 12 weeks to the day after knee #2. My mobility was pretty good by then, but I still got tired fairly easily.
Having said that, everyone's different. If you're thinking Disney World with all the walking & standing in line, maybe not. (Ditto D.C.!) Be prepared to skip some things or say to your fellow adult traveler, "Please take over. I'm going back to the hotel to put my legs up."