G'day CF & FF,
there has been quite a bit of discussion on this topic over the past couple of months...hit the search function and i'm sure you'll turn up some helpful info.
For me I'm happy to hold fuel for 3 months before burning it off in the car and starting again...others 2-6 weeks.
Two years ago I left a tank of shell optimax in the Harly parked up for 9 months and came back to a carby full of green jelly and a tank full of green liquid that smelled like kero...first time I'd ever had fuel go off. (I was in a company vehicle)
Last year it sat around for 6 mths with premium and was fine...so I reckon 3 mths to be safe IMO
Others will have other opinions...see recent discussion on Premium v Standard unleaded
Happy searching
Rhys