Poorly implemented GPS receivers might lose track of time because of this.
Many servers in the NTP Pool are using GPS signals to set the time, either directly or indirectly from another server that listens for GPS signals.
The expected impact on users of the NTP Pool is very little or none at all. The NTP Pool monitoring system will detect any systems that are wildly off and have them removed from DNS responses within typically 10-20 minutes.
Most servers would also recognize that the “jump” in time from a potentially misbehaving GPS clock is too large and ignore it (the time would be set back to August 1999, most likely).
Most importantly, reasonably well written clients will poll 3 or 4 IPs and ignore the one that’s an outlier by decades, recognize that the time returned is many years older than the earliest possible manufacturing date of itself or that the jump in time is too large and again ignore it.
The time of the rollover is midnight UTC on April 7 (so late afternoon April 6th in California or the morning of April 7 in Asia). We will be checking the NTP Pool monitoring data for any signs of problems through the day.
See also the NTP Pool community discussion.