I have an insulated big box propane smoker with 2 chip trays, I soak one trays worth of chunks. The first tray starts smoking within 20 minutes and lasts about an hour, then by the time the water evaporates/burns off/dries, etc... on the wood in the second tray, they start smoking. Doing it this way gives me fairly consistent smoke for up to 2.5 hours.
Bluto tells it best so far. Dry wood smokes almost immediately. Wet wood smokes later. What you get from wet wood initially is a steam burn off and a later smoke. Seems reasonable. .