That's what i was thinking as well, his temporary documents may very well already be null and void.WP and TRV should actually no longer be valid. Sometimes it isn’t automatic but there is a risk that when you show up at the airport you won’t be allowed on the plane with the TRV.
It should be the moment he received his COPR.
This is why the PRTD is a much better idea, also gives IRCC a chance to ensure everything in the system is reset so that when he's going through immigration, everything is up to date on file and his landing is smooth.