You can add BOOSTane octane boosters both before and after the fuel has been added to the tank.  Ideally, you add BOOSTane right before you pump your gas.  This will result in an immediate mixture.  However, BOOSTane’s carrier will enable a complete blend, even if it is added after.

Only poor fuel quality w/ ethanol in my area

This is a very common occurrence in higher performing vehicles, even from the factory, that have a higher stock compression.  

The issue typically lies in the quality of our available gasoline at the pumps, these days.  With the advent of ethanol supplementation in our fuels, we are now faced with an unstable/unreliable fuel.  This ethanol has a much high rate of degradation due to its hygrospscopic nature (naturally affinity to absorb water from the atmosphere and cause phase separation).

Our engineers over here at BOOSTane assessed that problem and were able to implement a proprietary carrier that not only keeps our active ingredients suspended in solution, indefinitely, enabling us to deliver the octane you desire, but also slow that degradation and phase separation of our daily gasolines.

Therefore, for your 91 octane, I would recommend 1/2 can BOOSTane Premium per full tank of gasoline.  This will roughly get you 95/96 octane, and enough to prevent that timing retardation.

Let us know if you have any other questions.