Pushing the whole company into the past on purpose
Every six months or so, this neat group called the International Earth Rotation Service issues a directive on whether there will be a leap second inserted at the end of that six month period. You usually find out at the beginning of January or the beginning of July, and thus would have a leap second event at the end of June or December, respectively.
Ten years ago, in January 2015, they announced a leap second would be added at the end of June 2015. The last one had been three years prior, and when it happened, it screwed things up pretty bad for the cat picture factory. They hit kernel problems, userspace problems, and worse.
This time, I was working there, and decided there would not be a repeat. The entire company's time infrastructure would be adjusted so it would simply slow down for about 20 hours before the event, and so it would become a whole second "slow" relative to the rest of the world. Then at midnight UTC, the rest of the world would go 58, 59, 60, 0, and we'd go 57, 58, 59, 0, and then we'd be in lock-step again.
So how do you do something like this? Well, you have to get yourself into a position where you can add a "lie" to the time standard. This company had a handful of these devices which had a satellite receiver for GPS on one side and an Ethernet port for NTP on the other with a decent little clock on the inside. I just had to get between those and everyone else so they would receive my adjusted time scale for the duration, then we could switch back when things were ready.
