In fairness, that does put a rather different complexion on it, as OP didn't mention it needing to be done the preceding day.
"After a random delay of up to a minute, the oven turns on." As described it merely gets you a few random seconds pause after pushing the button and setting temp, thus screams of "cheat mode", which seems at odds with your description. Setting a timer to come on tomorrow at roughly 3pm doesn't feel like it's quite so blatantly breaking the spirit of a rule for the day, as press then maybe you wait 1s, maybe 59s. Whether a next day timer is also bending the rule is a much finer judgement...
So now I'm not sure how to interpret.