important to note:

This is a long‐term commitment. You can remove yourself from the pool whenever you like, but due to misbehaving NTP clients and misguided configurers resolving a singular pool IP once and hardcoding it in a fleet of devices, it can take months, years, or forever for the traffic to stop. (I e‐mailed Dave Plonka about the 2003 Netgear–University of Wisconsin incident recently, and apparently they still see a bit of traffic from these routers.) For a long time after removing yourself from the NTP Pool, you will continue to get hammered on UDP 123 for years.