It's true that the new UA has adopted the 40-minute mainline turn from CO and that's not only annoying but leads to sloppy delays and way too much back-and-forth by GA's coming onboard.

But, that has nothing to do with the issue at hand which appears to relate to aircraft substitutions. Unlike mainland domestic flights xHUB's where there may be a spare or rearranging is possible, it's a little but more challenging in the case of small out-stations like OGG. Delayed outbound to OGG means delayed inbound to the mainland and so on. UA may well know a day in advance that it's got a problem and can start maneuvering aircraft.

As others note, it's both an art & a science. Do we take one 60-minute delay or do we take 3-10 minute delays? Can we substitute a smaller aircraft and not bump hald the pax?

But, as to departure times, it's important to remember that there are last minute substitutions and when they're found, the aircraft goes as scheduled.