If you wanted a slightly deeper, more philosophical element… you could have it where every certain amount of time, you lose money (such as by operating cost).
Great idea, I mean, how else would there be challenge to the game if you can spend as much time as you want until you decide you want to get an upgrade? Anyways, my goal was to avoid making it be a hidden objects game masked as a simulation game, but now that I think about it, that might be ok.
