I found a post on Gnome Stew that I couldn't disagree with more. My position on detailed world building is that it's not necessary, and you don't have to do it if you don't enjoy it.
The writer suggests writing a detailed schedule and description of a village that's not even the central point of action for a fantasy game. I've argued why that's a waste of your prep time, and explained how to get the same effect without all the effort. I wrote how to use conceptual "white space" to fill in those details in the players' imaginations here. Remember, I'm a huge prep GM. I prep a lot. I'm not afraid of prep. I just don't want to suggest GMs prep a pile of stuff that's not going to be used.
The result of that work is a chunk of rich greybox text that ends in "so what do the PCs do now?" I've argued why that's a waste of your table time. While color scenes are valuable sometimes, I advocate cutting to the chase.
The greybox text is nice, and has a strong feel of depth. But you don't need to invent a calendar and routine for the town to get it, or engage in amateur civil engineering to give the town a purpose and ecology to support it and this that and the other... Fantasy heroes aren't urban planners. They're generally adrenaline junkie vagabonds with a do-gooder streak, incredible luck and martial skill. Fantasy adventures don't care about the town calendar or the history of the village wall... unless it's relevant to the dramatic action.
Your story doesn't care about a lot of the town's details. It cares about what the down does for your story.
Your NPCs don't need a detailed calendar. If you decide today is washing day, it's washing day. Better, if the story would be more fun if it were washing day (say there's a foot chase down side streets), you can make it washing day without throwing away a good half hour of work because you didn't commit to a calendar.
I don't mean to be cruel to the author, Patrick Benson. The article is well written, and it supports a world building style of GMing. That style of GMing creates results that are just as good as the results created with my advice, it's just slower.
If you are the sort of GM who really enjoys world building, go read the post and follow his advice! Just be aware that the results you're getting don't require that much work, and you should only do the work if you enjoy it -- or if you plan to publish a campaign setting book!