POD: Any time after 1900, say the first major auto racing wreck.
Challenge: introduce better tech & design ASAP. That means seat belts, crush zones, fuel cells, but also (frex) getting rid of the yumps at the 'Ring,

& the trees trackside there,


& hay bales as barriers.
It means early introduction of hard helmets, HANS devices, & soft walls. It means track marshalls with fire extinguishers. It means firesuits.
So: when can any given tech be introduced? Who'd demand it? Who'd develop it? And who'd introduce it?
Outright bans of formulae (like Group C or AA/FA) are out of bounds; indeed, if you can save AA/FA & still be safer...


Avoiding the NHRA nitro ban would be good, too.
What do you say, racing fans?