Normally, I check the oil before I start the car when the car has been sitting for a while, but I've heard from others that the oil should be checked 10-15 mins after you turn your car off so that you can get an accurate reading when the oil is warm. Is that True?
The best practice is when the engine is warmed up, shut the car off and wait 1-2 min for the oil to drip to the oil pan and then read the level.
IMHO what's important is that you periodically check the oil - not which method. With modern 0W - 30/40 oils, there isn't a whole lot of difference. I've made a habit of doing a walk-around look at the tires and such and an oil check when I fill up. I figure, I'm standing outside next to my car anyway, and it takes about the same time as a fill-up.
What does your owner’s manual say?
According to the good folks at Consumer Reports, it varies by manufacturer.
I personally doubt it makes enough difference to worry about.