Comment by yardstick

From my own experience managing large numbers of routers, and troubleshooting issues, I will never use pool.ntp.org again. I’ve seen unresponsive servers as well as incorrect time by hours or days. It’s pure luck to get a good result.

Instead I’ll stick to a major operator like Google/Microsoft/Apple, which have NTP systems designed to handle the scale of all the devices they sell, and are well maintained.