oil pressure

[V4F]

I had a guy ask me how long it takes to get oil to the mains on stock "A"

his report --- but we can't get that oil pressure hole screw out while in the car even with carb etc. off (it's been rounded off in slot and is stuck solid).
Do you know if the time to get oil to all chambers (and therefore all main bearing tubes) is written anywhere, so we can understand if this engine is pumping enough to do that job. We ran it once for over 3 minutes and there was very little in the back chamber by then.
I know it's usually all happening behind a steel panel, but thought somewhere it would be written what the original specs were, so that we can compare it to that.
If not, I know we will have to pull down and start checking everything, but it was driving nice and except for the ticking, we believed it was all OK and was going to let her keep driving. When we saw how long it was taking oil to get into the 3 chambers we don't think it's safe to bolt all back up and drive.

any help greatly appreciated ............. steve