I’m not sure about that, I’m not very familiar with the consequences of time travel. What I meant was that on a villagers birthday, for example Bangle on August 27, you could visit my island to celebrate with Bangle, and if she lived on your island too you could celebrate with her and it would count twice. It’s not the same as Celeste, KK Slider, or Redd (can only visit once, regardless of island).
When I was working towards this goal I’d look up what villager had a birthday on the day, then post here asking if anyone had that particular villager on their island and if I could come visit. More than once I was able to visit the same villager on two separate islands.