Hey, this is fun, I'll pitch in... It completely depends on the mission circumstances. Yep, completely solo in a SxS, I probably have some extra to burn off on my side, thereafter, probably at 1hr intervals. Two up in weather, I'm probably going to run the first 2/3 at 1hr intervals again, but that might change to 30min for various reasons. Leading a flight long cross country, the 30min ops check is the rule. The first one will come at the top or bottom of the hour and thereafter. The tank change should be a whole lot more than just changing tanks, but all kinds of house cleaning tasks. Is the airplane configured as it should be and performing nominally. Are all the parts still attached? Is there a stream of blue coming out of one of the fuel caps. Are they both still there (after a fuel stop)? Do I know where "nearest" is... etc, etc. That is a tank change.