Tracking BBT: before or after you get out of bed?

Jennifer • TTC for 3 years (1 blocked tube), 2 MC
I've read that you should do so before you even move a muscle. However, a fertile myrtle told me that it's okay to take your temp after you get out of bed if you forgot to check it initially. 
How much of a difference do you think it would make if I got up and took a few steps to grab my thermometer as soon as I woke up?
I'm just wondering if I've been doing it wrong this whole time and if I adjust to taking my BBT in bed if I will notice a difference.