TL;DR Best fix is a better connection, but workarounds can help. Timing issue may vary by the situation.
Duplicati (and maybe any Internet backup software) is going to have trouble with a bad connection, so if you can possibly improve that it might be very good. Programs can sometimes work around slightly bad connections using techniques such as reducing file sizes (as was suggested) or increasing their retries.
Choosing sizes in Duplicati
–dblock-size (a.k.a. Remote volume size in the GUI)
–throttle-upload (but use carefully because it’s buggy in current beta releases – should be OK next beta)
If you can show poor results on an Internet speed test, your ISP might also be able to help, although they might want some troubleshooting to make sure it’s their fault and not in your equipment, e.g. weak Wi-Fi.
Point-in-time backup can come very close to actual time on the backup label if one has –snapshot-policy make a snapshot (has OS and other requirements) but otherwise files just get picked up as backup runs, and the longer the backup runs the less known it becomes when a given file was actually read to backup.
Agree that care should be taken to not make the timing less accurate than current, if this feature is done.
There is possibly already a timing inaccuracy in the synthetic filelist idea for an interrupted backup. This tries to show what was in the last backup, updated with whatever was backed up before the interruption.
There’s probably a risk of the synthetic filelist view of files looking like one that got to finish updating files, however there are those asking to restore anything backed up, even if other files aren’t yet. It’s a tradeoff.
Stop after Upload raises similar issues to what-if-network-fails or what-if-we-intentionally-do-it-in-chunks.
I guess it depends on how particular one is. Sometimes one just wants the latest available copy. If not, a search among different recent backups might be needed to find a favorite. Check contents until pleased, however if you happen to know the time you want instead, test the restore and see what file time you get.
Certainly there are cases (especially in business) where what you want is set by time, but it’s not always.