As long as you checked the villager's house after the Tumblr user left (after the WiFi session is ended) and it says, "Moved Out," it's fine to time travel back to today! The message won't technically be there, since the villager's house will be gone. But the villager should move into the Tumblr user's town just fine. The villager has already been convinced, and the other game already has the villager's data.
TTing backwards any amount of time (other than minutes or hours within the same day), counts as one day forward. The message and Prince's house will be gone, and yes, he will still go to the other user's town. Basically once the house says "Moved Out," you're free to do as you please.
Thanks truly a lot for your answers, it'll help me a lot! Just a last one to finish this for all.
Does this villager, once the message "Moved out" settles up, be somehow "reserved" to the other user? What I mean is, if somebody else tries to get my villager on his actual moving date, will they succeed? And what if my villager decides to stay in town, does this means that the other user will get a... "copy" of my villager?
Sorry if this is confusing, hAH,,,