I would keep the tip of the flame on the neck top of the shoulder. As for the time, that I do not know. I haven’t used a flame annealer for a long time now, but I would look into other people, respectable people that you can find on YouTube or places like that that can describe that.
There is a...
Agreed.
I have never perceived them as a good choice for cartridges with that much recoil.
Not that they can't handle more, but for me, I see them as 308 Win and Creed case capacity on down.
I have one on a 6GT and another one on a 20 Tactical-Both specialty pistols.
Varget and H-4895 are the two powders I use for 308 Win's, whether short, sub 16" or 30 inch barrels.
Factory Remington barrel chopped on my center grip XP-100 (H-4895 with 155 and 172's - Easily sub 1/2" MOA)
155's off of a bipod both times (100 yards and 500 yards on steel).
My F-TR Rifle...
I think you are good to go, once you move your group from your top pic to the left.
Maybe...1 click down.
Once you do your cold bore testing you will know.
Yet, for the distances you are shooting, a 1/4" (if that much high) is a nothing burger😁