I just wish they'd go for even a vaguely close estimate rather than something that feels completely wrong. Like I had 3 or 4 times in a row tried to do an update for my mac and once the download started it said something like 18 hours so I left it to go do other jobs and came back 2 hours later to find actually it had only take 1 hour and then it had waited for me to put my password in to finish and when I hadn't it'd shut down and ended the update. So I had to boot it back up and re-do it. After the third time I just sat and watched it for the 1hour it took (compared to the anywhere between 4-18hrs it claimed - it never claimed 1hr, even at the fastest it said 4!) just so it wouldn't shut down if I didn't put my password in fast enough