If an apology could travel backward, would the hurt still be necessary for the apology to exist?

An apology sent backwards would arrive before the harm and make itself unnecessary, which raises the odd question of whether it would still mean anything. Part of what an apology carries is the acknowledgement of a real injury that actually happened, so removing the injury would remove the substance of the regret. Repair depends on damage.

The usable version is about the present. You cannot apologise ahead of time, and you can prevent the harm you can already foresee. Where you know something you are about to do will hurt someone, the choice is between doing it and apologising or not doing it, and the second is nearly always available.