It takes time for the ECU to react to fuel and advance the timing. You can't just put several litres (few gallons) in and expect a result, you need to be consistent. The maximum tune is also the maximum, so if you're tuned for 93 and put in 100 you'll only get 93 equivalent advancement of timing.

Here in Europe fuel is normally measured in RON (research octane number) and not AKI (anti knock index - an average of RON and MON) like the US so the numbers below look odd.

Fuel is widely available in 95 RON and 98 RON variants. Our P cars are tuned to 98 RON and I run mine on this wherever possible. It gets better mileage on similar trips and 'probably' goes faster.

If I put in a tank of 95 then it immediately runs worse and it takes several tanks of 98 to get back to where it was. As does putting in old 98... so fresh correct spec fuel is the way to go.

And at 8.99 USD a gallon you've got it good :-) the cheapest fuel is more expensive here.