I didn't keep time with a stopwatch, but I tested the tube multiple times, for a few minutes each time. I didn't want to believe it was really bad, and I have had a number of tubes that gradually "woke up" after sitting on the tester for a while. I also tested the filament for continuity more than once, again, not wanting to believe my eyes. The white getters convinced me I was wasting my time on a gone-to-air tube. The visible rust on the tube elements is also consistent with air (and moisture) getting inside.
That's a sample of one, so take it for what it's worth
Phil Nelson