I generally let the car sit at least 3 minutes. It's also worth noting the dipsticks on our cars are funky. One side of the dipstick will typically say one thing, like full, and the other side of the dipstick will say anywhere from like low to 1/2 full. I'm pretty sure this is because of the way the dipstick sits in the oil pan. I generally split the difference between what the back and front of the dipstick read, better safe than sorry.
There have been times where I've checked the oil level and it'll say like 1/2 full, double checked, yup still half full, third check out of boredom? All of a sudden barely any oil on the dipstick. The dipsticks on our cars just stink, there's a few threads on the subject, here's one