The error mentions hours and minutes, not packages - because this failure is about time itself. apt is refusing a repository file that appears to come from the future. Fix the clock and the error disappears without touching a single repository.
Of all apt errors, this is the most honest one: "Release file is not valid yet" tells you the exact problem and even counts down how long apt would wait. Your PC's clock disagrees with the repository's timestamps, and apt sides with the repository. This page shows how to check the clock, switch automatic time sync back on, and deal with the two repeat offenders - dual-boot machines and a dying CMOS battery.
Every Ubuntu repository publishes a signed Release file stamped with the date and time it was created, and a date until which it stays valid. apt checks that stamp against your PC's clock. If your clock is behind - say the machine thinks it is Tuesday while the repository file was signed on Thursday - apt concludes the file is "from the future", refuses to trust it, and prints not valid yet along with how long it intends to wait. It is a security feature working correctly against a clock that is lying.
The good news: nothing about your repositories, keys or installation is damaged. Fix the time and the same command succeeds, usually within a minute.
date. Compare it with your phone. A wrong year, month or a few hours' difference all count - apt cares about all of them.timedatectl and read three lines: Local time, Universal time, and System clock synchronized. If synchronized says no, the PC is not correcting itself from the internet.A clock that is wrong again after every shutdown is not a software setting - the small coin battery on the motherboard (the CMOS battery) that keeps time while the PC is off is dying. It costs very little and any computer shop can change it in minutes; on a laptop it may need a service visit. Until it is replaced, the quick workaround is the same each boot: connect to the internet, give NTP a minute, then update. Do not fight it by editing repository files or disabling apt's validity checks - the clock is the problem, and it is also the cheapest fix on this page.
The video shows the failing update, the clock check and the successful rerun on a real Ubuntu machine.
▶️ Watch Full VideoRepository Release files are digitally signed and carry a creation date and a validity window. apt compares those dates with your system clock to make sure it is not being fed an old, replayed or tampered package list. If your clock is set before the file was created, the file looks like it comes from the future, so apt refuses it and reports that it is not valid yet.
Check the time zone with timedatectl, not just the clock face. If the zone is wrong, the displayed time can look right while the underlying UTC time is hours off, and apt works in UTC. Also make sure System clock synchronized says yes. If both are right and the error stays, the mirror you use may be mid-sync - wait an hour and try again before changing anything else.
Windows stores local time in the PC's hardware clock while Ubuntu stores UTC and converts for display. Each operating system reads the other's setting as its own, so the clock jumps by your time zone offset on every switch. Enabling network time sync on Ubuntu corrects it automatically a minute after boot; the permanent cure is to make one system match the other's convention.