when he still thinks there are 20 minutes still left in the gearbox.
That's a pretty big assumption you just made. Do you know that to be a fact??
Most (perhaps all?) S92 pilots that I know did not think the aircraft had 30 mins run-dry before the accident. The RFM was clear (less than 5 psi = Land Immediately). The details of certification requirements are not something your average pilot would ever look at. The FlightSafety pilot training courses never mentioned 30 mins run dry, but I can't comment on the Cougar course!
I actually think they were presented with some unusual indications that led them to believe that the lack of oil pressure might be a false indication.
But until CVR extracts are made public I do not think we will know for sure.