How long does it take for petrol to go "off"?

[Casper]

Just curious, has anyone got any information on how long it takes for premium fuel to go "off" and lose its kick?

Reason I ask is I hardly ever drive my XR these days (I'm either interstate or working from home so no need to) and its not uncommon for it to sit for weeks on end without being driven.
At the moment its got a little over 1/4 of a tank in it which was put in back in mid December (yup, Ive used less then 3/4 of a tank in over a month) and I'm curious to know how long before it goes off and at what rate it degrades.