I put in a good bit of time into each session, with maps, handouts, props, weather tables for the next few months, encounter tables, NPCs statted out with combat options considered, plaster dungeon pieces assembled, etc.
Fortunately, I never throw away an NPC, magic item, plot idea, etc., and have no problem with filing off the serial numbers and reusing them, so it doesn't take as much time as it could. It allows me to spend more time on the handouts, props, and other creative timesinks that I enjoy more.