I had a 14.2+current problem (and thread but can't edit old posts/titles) now also on 15 stable & current. After I ran LILO and rebooted, LILO said 'timestamp mismatch' and showed no menu (I have several OSs) and wouldn't boot. No matter what I tried, it wouldn't fix. I set BIOS clock two days ahead (though BIOS & OS times were identical beforehand... my BIOS is set for zone so OS gets it exact so presumably NTPD changes remain exact in BIOS). I zeroed entire drive & boot sector, rebuilt partition table, reinstalled LILO. Same happened and I tried many times.

LILO timestamp mismatch test should probably be optional: more a desktop users' hindrance and servers have timekeeping tools.

Some people didn't read and wildly speculated I had different BIOS & OS times though originally stated they're identical: nevertheless I triple-checked and reset BIOS which clearly changed nothing. I think I also turned off NTPD but of course the problem actually has nothing to do with (identical) time.

The problem may be known (and discussed various other places) some SSD/M2/NVME drives stopped working with LILO: they used to just fine before changes in later 2021. After that apparently SSD/M2?NVMEs are specified differently in a way LILO hasn't been updated for.

Meantime I installed GRUB2 (works but quite hate it).

What do I need to do to use LILO again?

LILO's "timestamp mismatch" is not about your system time or BIOS time.
The LILO boot process is done in a few stages. When you install/update LILO, it updates all the stages and writes a timestamp inside each of them.
Usually when you get the "timestamp mismatch" it means that the LILO first stage (containing a specific timestamp) is trying to load the second stage in order to start it, but founds out it contains a different timestamp.
This error typically means that the last LILO update did not update all the stages correctly, or that one of the disks contains an old LILO installation.

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That's exactly the catch - in AD 2021 the kernel developers changed something in the NVME management, and LILO hasn't been updated for, because it's last release was made in November 22, 2015. Yes, nobody updates LILO today. Nobody updates LILO anymore.

I wonder what's so complicated to understand on that LILO, ELILO and SYSLINUX are abandoned by their authors since long years, even years before of Slackware 14.2 release?

Read: this horse is dead, Jim! Stop kicking those bones!

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After zeroing entire drive (dd to plain block device itself, blkdiscard & similar UNIX/*BSD trim) & entire boot sector & reinstalling many times but always getting same result, seems case of something else.
        I heard others might've been maintaining LILO but maybe that was only until 2015... SYSLINUX was updated a couple years ago.

Take over its development.

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I made a mistake: they changed it in 2016 which immediately broke LILO for some, but others including mine worked into 2021, though they may have also changed something then.

how does LuckyCyborg boot ?

It is a well known fact that he prefers grub.

regards Henrik

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Is this the same machine which regularly gets a zap of static electricity powerful enough to reset the BIOS?

Not since a year or so ago.

Apparently no choice but to switch to GRUB2: solved that way (not in the code).