Thanks for the clarification. I think the best you can do us what’s mentioned in the post below, but be aware that if your connection is REALLY bad (or down for a long while) it could make a normal 30 min. backup appear to take 30 hours (due to the retries).
And of course, if the computer is shut down (not sleep, but actual power off) the backup will be aborted - but will pick up where it left off when the next scheduled job runs kicks off.