IIRC windows doesn't run ntp by default, it runs some propretary w32time service instead. I think it has an ntp client built in, but I'm not sure if it can be an NTP server out of the box.

If your Windows Server Clock Drift cannot sync time from an external NTP server and is in a warning or failed state while running, then this post may help you. Syncing the time includes running “w32tm ...

Every few years, a Leap Second needs to be added to Coordinated Universal Time (UTC), so that we keep the time of the day as close to the mean solar time as is possible. On a Leap Second Day, an extra ...