Wrong schedule running when duplicating start times

That's fine. I knew there was likely to be other factors to take into account so it was just a suggestion.

The point I made with the frequency was to try & show the more obvious impact - we've come across this more than once on the forum - but there is a more 'insidious' aspect we've come to know as 'schedule creep':

It could be due to resource limitations that a job may start a few minutes late - it will now always run a few minutes late. If it gets delayed again ......etc etc. This may well be more than a few minutes if no resources are available due to the fact that other backups are running for hours. Due to the fact that we (as backup admins) always seem to have a lot of backups to squeeze into the smallest possible time then, if something is delaying backups, we could be losing a 'window of opportunity' (pun intended!) to get our backups done earlier.