It really depends on the gas quality. I've had it happen to me in as little as two weeks, but your mileage may vary (We only have access to the E10 stuff down here, so ethanol free gas might last longer).
The simplest way to avoid it is to just go out there and
drain the float bowls, which will take you maybe 5 minutes.
You shouldn't need to run the bike until it dies -- both methods accomplish the same goal of getting all the gas out of the carburetors. When you need to start it up again it will take a bit of cranking to fill up the carburetor bowls (it will seem like it's not going to start for a while), but as soon as that's done it should fire up with no problem.
If you're worried about draining your battery too much with all that cranking, you can get a simple hand/pump vacuum at your local hardware store and use it to apply vacuum to the vacuum line on your petcock for about 2 seconds to get some gas into the bowls. Don't keep it on there too long, as you could end up with gas leaking past the float bowl seals if they've been sitting for too long (they dry up and shrink a bit if the carbs are empty, so the first time you fill them up they may leak a little).