1 pointHave you tried the "Options" section of your script? There's also scheduling options there, which only apply to that script (though the defaults reflect the Schedule settings in General Prefs, which might make you think otherwise...) and so would have no impact on manual backups. Set your "Start", "Wrap up" and "Stop" times to suit your working practices and required backup window and you should be good.
1 pointI suggest you simply remove the systems from the backup schedule on the weekend, therefore when you boot the systems on Monday morning there won't be a slowdown. You obviously already know how to launch a backup job manually, so just do that.