Seen on a Windows 10 WSL2 Ubuntu install:
E: Release file for http://archive.ubuntu.com/ubuntu/dists/focal-updates/InRelease is not valid yet (invalid for another 2d 21h 4min 21s). Updates for this repository will not be applied.
E: Release file for http://archive.ubuntu.com/ubuntu/dists/focal-backports/InRelease is not valid yet (invalid for another 2d 21h 4min 56s). Updates for this repository will not be applied.
E: Release file for http://security.ubuntu.com/ubuntu/dists/focal-security/InRelease is not valid yet (invalid for another 2d 21h 4min 2s). Updates for this repository will not be applied.
caused by the Linux system clock lagging behind Windows:
$ date
Fri Jun 18 15:08:28 BST 2021
Fix:
# Show the rtc
$ sudo hwclock -r
2021-06-21 13:41:16.938054+01:00
# Set the hw clock
$ sudo hwclock -s
# Verify
$ date
Mon Jun 21 13:41:25 BST 2021
Real hardware faults / CMOS battery failures / Y2K knowledge to the rescue!