One of the things you need to remeber is that the oil is heavier then the fuel, so it will settle after time. When I leave pre-mix in over night or more, I tend the shake the bike around prior to starting it to mix the oil and the gas as much as possible again.

I have tested Belray 7SI in a bottle in my apartment and no separation happened after a month.

I had 20liter cans with premixed( I think its TTS) gas standing for half a year in my garage and no separation occurs.

As I've seen old gasolin, without mix go bad, I usually put the old unused premix from last year in the car and give the NSR fresh gas, but I can't see any separation happening.
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Poul
"If Life Gets Boring, Risk It!"
MC21SE, KISS box
MC21SP, HRC box, racing loom