"I do not think a few weeks would be considered too late. But in the end, if you feel too much time has passed, you can always make the note to thank them the next time."

It was a big change for him. While WangJi wouldn't have had much of an issue if it was something big to thank someone even at a later time, it was new to him so he didn't want to create added pressure which might cause him to rethink this.