What does “Release file for […] is not valid yet (invalid for another […]). Updates for this repository will not be applied.” error mean?

An error message indicating that the release file is not valid yet.

$ sudo apt update
Get:1 http://security.debian.org/debian-security buster/updates InRelease [39.1 kB]
Get:2 http://deb.debian.org/debian buster InRelease [122 kB]
Reading package lists... Done
E: Release file for http://security.debian.org/debian-security/dists/buster/updates/InRelease is not valid yet (invalid for another 28d 16h 59min 44s). Updates for this repository will not be applied.
E: Release file for http://deb.debian.org/debian/dists/buster/InRelease is not valid yet (invalid for another 28d 11h 11min 20s). Updates for this repository will not be applied.

System time.

$ timedatectl
               Local time: Fri 2019-08-09 22:40:02 GMT
           Universal time: Fri 2019-08-09 22:40:02 UTC
                 RTC time: Fri 2019-08-09 22:40:03
                Time zone: GMT+0 (GMT, +0000)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Release file.

$ sudo head -14 /var/lib/apt/lists/partial/deb.debian.org_debian_dists_buster_InRelease
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA256
Origin: Debian
Label: Debian
Suite: stable
Version: 10.1
Codename: buster
Changelogs: http://metadata.ftp-master.debian.org/changelogs/@CHANGEPATH@_changelog
Date: Sat, 07 Sep 2019 09:51:20 UTC
Acquire-By-Hash: yes
Architectures: amd64 arm64 armel armhf i386 mips mips64el mipsel ppc64el s390x
Components: main contrib non-free
Description: Debian 10.1 Released 07 September 2019
Notice the time difference, we are in the past now. This can happen when you restore the system from a snapshot, therefore the time indication will be incorrect for at least a while.

Synchronize time or wait for a while till the system updates it from a remote source.

$ timedatectl
               Local time: Sun 2019-09-08 09:48:49 GMT
           Universal time: Sun 2019-09-08 09:48:49 UTC
                 RTC time: Fri 2019-08-09 22:40:33
                Time zone: GMT+0 (GMT, +0000)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

Problem solved.

$ sudo apt update
Get:1 http://security.debian.org/debian-security buster/updates InRelease [39.1 kB]
Get:2 http://deb.debian.org/debian buster InRelease [122 kB]
Get:3 http://security.debian.org/debian-security buster/updates/main Sources [41.9 kB]
Get:4 http://deb.debian.org/debian buster/main Sources [7,832 kB]
Get:5 http://security.debian.org/debian-security buster/updates/main amd64 Packages [82.1 kB]
Get:6 http://deb.debian.org/debian buster/main amd64 Packages [7,899 kB]
Fetched 15.9 MB in 7s (2,148 kB/s)
Reading package lists... Done
Building dependency tree
Reading state information... Done
107 packages can be upgraded. Run 'apt list --upgradable' to see them.

This issue is the opposite of the one described when I described Valid-Until behavior in How to install packages using repository snapshot.

ko-fi