I recon only perhaps a minute from filling to screwing in the sensor to achieve a seal, then turning the engine over.
Given normally the oil pump would be left for a couple of months and not needing re-priming I cannot see the oil draining through the pump gears that quickly?
I'm using 20/50 which is not really thin?

I'm thinking move to vaseline next....also gives me a change to inspect the gears, (should i need new ones after 10K miles?) and pump for damage and freshen up the face to give a really good pump performance - given its the first time its lost prime in 35 years of being left for a few months and then started ok.

Thoughts?