Time Machine has been "Cleaning up old backups" for 24 hours - should I let it keep going?

I guess I have an unsatisfactory answer to when or if you should give up:

• I gave up and stopped a backup on one drive after 36 hours of "Cleaning up old backups."
• A different drive did "Cleaning up old backups" for a little under 24 hours, and then proceeded as normal.
• A second attempt with the first drive did around 12 hours of "Cleaning up old backups", and then proceeded as normal.

So: if it's 24 hours, it could definitely still be working, especially with a new external drive or a lot of files moved (in this case 2.5TB), and you should let it keep going. 36 hours? I don't know. Maybe that had failed and needed cancelling, or maybe I gave up "too soon".

My main point of curiosity here is how the same drive was taking 36+ hours the first time, before I stopped it, and completed in around 12 hours the second time. That could mean, A) it had failed and it's good I gave up, or B) the first 36 hours helped clear a lot and made the second time faster. I don't have the knowledge to distinguish if it was A or B.

For Disc Space: on the iMac, there's about 600GB free (of a 2TB Fusion drive), but there's a lot in trash. RAM: 8GB - I always vaguely intended to get more shortly after buying this, but never got around to it, and I'm not sure if I'll ever bother now.

The Time Machine worked on the second backup drive I tried, although something's weird with how it's timing things:

• From when I started the backup: it was "Cleaning up old backups" for at least 18 hours.
• At the 24-hour mark: it was backing up, with "1.31TB of 2.50TB - About 17 hours remaining."
• And at the 28-hour mark it was done: that "17 hours" took four. I wonder if that faster-than-expected speed was because it did just "re-map" some of those big video files that were already in Time Machine, just in a different location. I did understandably lose older backups, but it still goes back as far as October, and I'm fine with that.

So, anyway, in this situation, yes, if it's still "Cleaning old backups" after 20 hours, yup, it may just be taking its time and it may still wind up working.

And now I've started it again on the other drive (that one is somewhat less reliable, in that every few weeks it hangs and I need to unplug it and then just plug it back in again) - the Time Machine backup that I aborted after 36 hours before. Possibly relevant: this less reliable drive is also the one that's always connected to the computer, whereas the one that worked after 20 hours is swapped back and forth every two weeks - so presumably the one that worked didn't have as many snapshots (is that the right word?) of previous computer states.

Anyway, I'll try to keep track of how long this one takes; I'm also curious if the 36 hours this drive already did of "Cleaning up old backups" counts as work already done, or if it'll be starting over.

Thanks - no, no progress bar. Just the vaguely grey morphing bar showing it's in progress. Note it's not at the stage of actually backing up yet - it's still just "Cleaning up old backups."

Somewhere online I saw a way that I could perhaps reveal a hidden file and then use Terminal to see progress on the cleaning stage, but that's a bit beyond my comfort level.

Hmm, OK. I actually stopped the "Cleaning up old backups" after 36 hours last night, because my computer had slowed to a crawl for everything else and apps were crashing - so I pressed the X in Time Machine and, after that stopped, restarted the computer. I then restarted Time Machine with my second Time Machine external HD (and a more reliable drive, for that matter).

As of now, it's been "Cleaning up all backups" for 12 hours; I tried the "tmutil listlocalsnapshotdates", and got just five dates, going back only to 2022-01-21. I don't know if that means it's cleaned up to that most recent date or not. (If so, wow, this backup is losing a lot of the "time machine" part of this!: on the Time Machine drive itself, the oldest folder is 2021-03-25)

If Time Machine is just doing its thing and taking 12-36-48 hours is normal, then I'm fine letting it run its course; what I wish I were better able to determine is if something's not working and I should intervene.

For what it's worth I only use Time Machine with hard drives directly plugged into my computer. One stays always at my desk; there are another two that rotate between my computer, and my office at work, so there's a backup at a different location as well.

Side point: there is almost no "new" material in these backups - it's just lots of media moved to a bigger external hard drive. I *hoped* that Time Machine would just "remap" the location of the 6GB (or whatever) movie files, without needing to erase old data and copy in a "not-really-new" 6GB movie file. I *suspected* that it would indeed rewrite that, and I'd lose a lot of the Time Machine deep archive. My backups did go back a year or more, but I suspect now I'll only be able to go back a month or two.

Have I missed a simpler way to do this? Too late now, but it may help anyone else who stumbles across this thread in the future - not that that's likely the way Apple's forums now seem to stymie search ... (Original situation: 2TB external drive for media that was totally full; 2TB iMac at around 1.5TB, with 500GB of that also media that I'd rather have on an external drive; several 6TB Time Machine backup drives. New situation: 4TB external drive, that now has all of that 2TB of media plus another 500GB or so from iMac, same 6TB Time Machine Drives.)