This depends on wether like many T2s, get dawn phenomenon.
If you do, then doing the fasting test before lunch is preferable.
If you don't, then as long as you test at the same time every day before food, then you can see if your fasting levels are getting better.
However, if you know by experience what your fasting levels are, the pre meal, two hours after are a better guide to how you are progressing (or not!)
Keeping a food diary, with a lot of detail which includes your dietary intake, readings, carbs, and symptoms, portion size. Will help with your doctor decide on any treatment needed and of course dietary advice.
I don’t, I don’t care about that number anymore lol, I can’t control it so why bother, I measure after my morning workout and breakfast, I’m usually good then
If you wait until before lunch there are many factors other than not eating any food that can raise or lower your levels, such as activity of any sort, which may vary from day to day so your readings could be inconsistent. If you want a true fasting reading, it is best to do it as soon as you get up before showering etc. As others have said, get up, pee, wash hands, test.
I only measured my FBG regularly for a few days. I soon realised that if I got control of the spikes from meals then my HbA1C would come down quickly and eventually my FBG would follow.
It still isn't that low even though my HbA1C is now in the non-diabetic range ( 37 or 5.7%), but it is lower than it was during those first few days.
Any time between when you get up and when you eat would be a valid fasting level, but your actual level may vary over that period of time. Many people (me included) have dawn phenomenon, so waiting a bit would yield a better (and hopefully more accurate, or at least useful) result.