How long does fuel keep its octane rating?

[Evoluzione]

And what is a good octane booster to use?

I brimmed the tank on my snotter for a mapping session which was unexpectedly (there is always something though isn't there?!) cut short due to the 750 injectors maxing out.
It may end up being 3 - 4 weeks till It goes back with bigger ones fitted and I am worried about falling short of the mark due to stale fuel.
Any ideas folks?