Using Aquatica housing and Leak Sentinel, on a liveaboard, I'll set it up the night before and leave it sealed and pumped down all night. My camera battery lasts for at least 4 dives, so I only need to open the housing once a day unless I change ports, etc. But I agree, 20-30 minutes should be sufficient. I pump it down two cycles beyond the green light. Once I did have a small leak and it showed up within a few minutes, less than five.
Great addition to mental health diving with a camera.