What you need to "make time pass" is to do something the game registers. Basically, do a piece of a quest, progress a side story a bit or something after you left the castle. Just talking to a random NPC or shopping is not enough. It's also not enough to just start a side quest inside the castle, but if you continue it on the outside or pick up one in another town, then "time has passed" and you can go back to get some money.
The amount of quest-steps you take is somehow related to the amount of time and so to your income as well, but i don't know the details of that.