The component where delete takes care of unscheduling was merged in with pr #23
There are cases e.g., disabling a job, where it would be reasonable to save a job with at time in the past. I've looked into raising a warning using Django's Messages framework, but the request is not passed through to the ModelForm so don't think theres a case to build off of this work to achieve that.
Saving a job scheduled in the past doesn't cause it to run immediately.
I'm closing this request for three reasons