Very Strange. Yesterday (Dec 19, 2025) I started up my M2 Mac (MacOS Tahoe 26.2) after leaving it shut down (turned off) for a day or so and noticed that the time in the upper right-hand corner of the home screen, showed: Thurs Dec 18 17:19. Actual time (according to my home clocks, iPhone), etc.: Fri Dec 19 15:28. [Yes, I configure my devices to show 24-hour time.]
After waiting a while to see if the time-of-day 23+ hour discrepancy would fix itself, I shut the Mac down and powered it up again. A couple of times: no effect. Meanwhile, System Settings > Date & Time settings appear normal:
-
Set time and date Automatically on
Source Apple (time.apple.com)
24-hour time on
Set time zone automatically using your current location on
Time zone: Hawaii-Aleutian Standard Time [correct]
Closest city: Honolulu, HI - United States [correct]
…. but the date and time stayed wrong; offset the same to actual date/time stayed consistent.
Curious to see what apps might be effected, I started up
Maps – which showed a blank map
Weather – which also showed blank (no weather info at all)
Tired of seeing the wrong time-of-day, I went into Settings > Date & Time, turned off the Source (time.apple.com) and set the data & time manually. Well up to the correct minute; didn’t try to fiddle the seconds. Rebooted; date & time stayed corrected. Went back into Settings > Date & Time and restored Source to time.apple.com and rebooted again. Date & time stayed correct. It was getting late, so I shut down the Mac for the night.
This morning (Dec 20), re-started the Mac and found it keeping time accurately down to the second. The Maps app now works fine. But Weather still looks like this:
Anyone know how to fix the Weather app?
[Here’s my strange theory of how the Mac’s time-of-day clock got to be reset wrongly: when the Mac was re-started after being powered down time.apple.com was either down or glitching. Which could happen if time.apple.com isn’t actually attached to its own hardware clock, but hard-coded to be dependent specifically on NIST’s atomic clock ensemble of hydrogen maser clocks at NIST’s Boulder campus. Those failed due to a prolonged utility power outage (starting Dec 17 2025 around 22:23 UTC) as NIST’s atomic clocks progressively shut down as the campus heat-exchange infrastructure failed, backup generators failed, and the clocks’ battery backup systems failed. As I write this (Sat Dec 20 10:05) those NIST Boulder time servers are still down. NIST’s Gathersburg, Maryland and Fort Collins, Colorado servers were not affected, and are still up and running consistently. And time.nist.gov (global address for all NIST time servers) shows all services available.]