No, not at all.
This visual novel is not a sequel at all.
It's a companion novel to Adastra, focusing on the Moon Tour (in the game, this event is merely summed up in a few lines).
OK, so Interea takes place during Adastra (particularly those times when many months pass, because almost at the end of the game on lovers day, after Amicus and Marco "got intimate", the game suddenly went from Marco having quite a bit more time left on Adastra to barely a day left) There are obviously many more time-jumps throughout the game but I can't think of all of them now. Basically Interea takes place during those missing time gaps, correct?