I just had the same issue on two different routers running OpenWRT 23.05.2
Both had a 50+ days uptime.
Both were connected to the Internet
Both had ntpd running
Both had their clock set as January 2024 instead of March 12th, 2024.
In both cases, issuing the command /etc/init.d/sysntpd restart fixed the problem.
Which leads me to the question, why wasn't time being synced properly?
relevant info from /etc/config/system:
config system
option zonename 'America/Toronto'
option timezone 'EST5EDT,M3.2.0,M11.1.0'
config timeserver 'ntp'
list server '0.openwrt.pool.ntp.org'
list server '1.openwrt.pool.ntp.org'
list server '2.openwrt.pool.ntp.org'
list server '3.openwrt.pool.ntp.org'