tmutil status shows time remaining but Time Machine preference pane says "Calculating time remaining"

Question

all. I'm running macOS 11.4. I using a new Time Machine backup destination and want to know how long it's going to take to finish. The Time Machine preference pane continually says Calculating time remaining…. However, tmutil status lists a TimeRemaining property, and it seems to be going down consistently.

Question: is TimeRemaining reliable and if so, how do I interpret it.

man tmutil | grep TimeRemaining gives me nothing, as do man tmutil | grep Remaining and man tmutil | grep remaining.

Thanks!

Backup session status:
{
    BackupPhase = Copying;
    ClientID = "com.apple.backupd";
    DateOfStateChange = "2023-05-26 16:29:15 +0000";
    DestinationID = "A895A939-B045-4714-8C66-3CDF4D861BC1";
    DestinationMountPoint = "/Volumes/path/to/destination";
    FirstBackup = 1;
    Progress =     {
        Percent = "0.4298995862004921";
        TimeRemaining = 727679;
        "_raw_Percent" = "0.4298995862004921";
        "_raw_totalBytes" = 855037718528;
        bytes = 367580361381;
        files = 806898;
        totalBytes = 855037718528;
        totalFiles = 2533396;
    };
    Running = 1;
    Stopping = 0;
}

Answer 1

Ah. The TimeRemaining field is just the time in seconds.

It's hard to figure that out in the beginning when there's so much variability in the estimate toward the beginning. I found every few seconds, TimeRemaining would go down but not but sometimes by thousands and sometimes by just a few.

Answer Source 1: This answer, which I initially had opened but dismissed as not answering the question, links to a utility on GitHub. Especially helpful is this line:

READABLE_TIME=$(seconds2readable.sh "$TIME_REMAINING")

Answer Source 2: My backup finally is giving me an estimated time of 9 hours (after two days of running with no estimate). The output of tmutil is:

TimeRemaining = 33144;

And 33144 / 60 / 60 ≈ 9.20677

Answer 2

I don't know about this for Big Sur but on Ventura, you can just get a percentage of the backup and how much data has been backed up from the menu bar. (See Back up your Mac with Time Machine - Check backup status for more info)

To check that tmutil status gives you the right infos, you can check if the menu bar option is an approximation of Percent.