If you check your engines oil level immediately after driving then the oil level on the dipstick will appear low because the oil hasn't had time to make it's way back down to the engine oil pan.
You can check the engine oil as early as 10 to 15 minutes but If possible I wait for 30 minutes to check the oil after shutting the engine off.
Usually I have time to wait 30 minutes when I'm on a road trip because by the time I fill the gas tank back up, go in and pay for the gas, take a restroom break and even a meal break then the 30 minutes will pass by and then before I get back in the car I check the engine oil level.
So although 30 minutes would be best to wait when checking your engine oil 10 to 15 minutes is enough time to get an accurate reading on your engine oils dipstick.