I think 2-4 weeks is the right length for RMN events, yeah. I'm not sure the game has to be longer, though -- the focus could just be a game with objectives you don't need to complete in an exact order, or at all. There's plenty of Squenix and Bioware RPGs that are just "uh, here's a bunch of stuff to do. You have do like, 20% of it. Go.", which I think might work better for a tiny event RPG as opposed to "make a normal game and then do the terrible sledload of sidequests at the very end." (I just wanna go kill the final boss qq)