Can 5fu be injected on the day of scar revision surgery into a wound or is that too soon?

Injecting compounds that decrease healing in the first couple weeks when the wound needs to ramp up inflammation to heal appropriately probably isn’t a great idea, I’m sure the merits of this could be debated, but you risk having the would breakdown or not heal appropriately by doing that.
In recurrent keloids, it is sometimes appropriate to radiate the wound within 24 hours of surgery to help decrease the risk, but that is usually used when someone has had their keloid excised and tried everything else to prevent recurrence.
Hope this helps!