Hickory: Every 'five stronghold days'. Note that prestige and security affects how much tax you receive -- funds can be lost to bandits.
Soccorro: stronghold day? ummm ok... What is a stronghold day? :/
I know when the adventures (little quests you can assign characters to in order to get bonus items, exp, etc) each "day" is actually one of your party quests completed.
So let's say an adventure says "2 days" - if you complete two quests one after the other, your adventure will finish right then and there!
I THINK taxes are collected and salaries paid based on in game time passing.