3 months in the least.
I mean, the past wipes have been a little more constant than the awaiting future one. But really, this game should reach a point where it becomes stable so that wipe would be pointless. But with current features that just make hoarding items very easy, people will always be at an advantage as time goes on.
But for the last wipe, which was March - August, that's a little over 5 months. And this session has been over 9 months, which is too long with current features. So... 4 to 5 months sounds like a good option, maybe a little longer, if this ever happens.