I don't worry about it, so I don't check it often, but....To check the engine-oil level, my owner's manual says: "After warming up the engine and turning off...wait more than 5 minutes (my emphasis) for the oil to drain back into the bottom of the engine." The implication is that not doing it precisely this way would lead to a misleading result. It's easier to just check the oil first thing, before starting the engine. What's wrong with that?
I've never noticed an appreciable difference, one way or the other. One thing, if it's sim to third gen Prius hatchback: it really helps to remove and wipe the dipstick, then wait about 5 minutes before re-insert to check. This gives the oil a chance to drain down the dipstick tube I guess, makes it much easier to read; there's no smearing above the true oil level.
Blog Post | When are you supposed to check your oil, when the engine is warm or when it's cold? | Car Talk
