big sur – tmutil status shows time remaining but Time Machine preference pane says “Calculating time remaining”

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;
}