Hi there,
I know you are SUPPOSED to take temp at same time - I don't and still get the results I want. There are some fluctuations but I usually see patterns - ie when they dip and when they rise etc.
During the week I temp between 6am and 7am, on the weekend I temp at 9am. I find this works for me - I know everyone is different, and I think the more important thing is that it the VERY first thing you do - don't get up, move too much, certainly don't go to the bathroom etc. I don't talk or anything, simply roll over and the thermometer is on the nightstand. I can log everything on my iphone next to the bed too. Even if I roll over and go back to sleep again.
As long as you've had a period of 3hours + sleeping, so it has chance to drop to your basal (base) temperature. So it's no good after a nap for instance....
I might just be lucky, but this works for me... good luck x