https://www.npr.org/2025/12/21/nx-s1-5651317/colorado-us-official-time-microseconds-nist-clocks

But when a destructive windstorm knocked out power to the National Institute of Standards and Technology (NIST) laboratory in Boulder on Wednesday and a backup generator subsequently failed, time ever so slightly slowed down.

The lapse "resulted in NIST UTC [universal coordinated time] being 4.8 microseconds slower than it should have been," NIST spokesperson Rebecca Jacobson said in an email.