Yep, three main things that can go wrong apart from overflow: 1) daylight savings changes the clock by 1h 2) leap seconds 3) user changes the clock. This one

Yep, three main things that can go wrong apart from overflow: 1) daylight savings changes the clock by 1h 2) leap seconds 3) user changes the clock. This one is fun. Gathering telemetry for a big website, I sometimes see operations that were supposed to take a few seconds taking weeks. Most likely explanation is: user hibernates the machine in the middle and restarts several days later, or user changes the clock. That's also why using averages in data analysis tools and not percentiles will kill your data reliability when such an outlier occurrs.