I tried to leave my game running the first time I encounter this sort of quest, but no matter how long I waited this way the game just kept asking me to come back later. With a bit trial and error I found out that by come back later, the game was actually asking you to change screens a lot, and to go to different areas of the game and change your screen there, not by waiting in real life. For example when you were asked to wait and come back later to somewhere for something, you first have to right click your map and leave that place, and choose some other destinations, and preferably click through all walk-able areas there, and then leave, and choose another destination, and repeat, till you gone through all click-able areas of the whole town. The more places you clicked through the sooner the time passes and you will get what you want.