BBT timing - same time or 3hrs sleep?

I'm wondering what you all think would be more accurate. I have an alarm for 7am when I actually get up, but I find I frequently wake up sometime after 5am, roll over and go back to sleep. I don't do anything, no bathroom/water, but consciously change positions. (I actually wonder if I would even notice this if I wasn't so used to temping and wondering "should I temp right now!?" Ha) Would it be more accurate to temp at that early 5am (or 5:15/5:47/6:25, etc, whenever that time is as it changes) as I've had the "3 hours consecutive sleep," or follow the guidance "temp near the same time everyday" at 7am? Today I temped 98.3 around 5am and 98.6 at 7am. I'm aware my temp would likely continue rising if I were in bed longer, which again makes me question which is better!! If I take it early and at random/sporadic times, it's not likely to be accurate either, even if I did sleep consecutively before. TIA!!