So do I (disagree)!
You can check the oil level any time you like, as long as the engine isn't running, and the car is on level ground. If the engine has been running, leave it for as little as a minute before checking. After all, it's only a rough indication of oil quantity - it's either visible on the dipstick, or it's not. If it's visible, it's either high or it's low.
And always run the engine for a few minutes before changing the oil - the oil flows out much easier when it's warm.