46-year-old healthy male. Major Depression. Currently undergoing ECT every Mon-Wed-Fri. 7-weeks left. Can I take Percocet on the weekends only?

For what indication? I strongly advise that you only take Percocet as instructed by the prescribing provider to avoid complications. Be sure to inform every healthcare provider you're seeing of all madications on your list including OTC.
Defer to psychiatry. I would check with your psychiatrist about this.