We don't have that rule, though we have the three year terms. I've been serving longer than that, but how long I don't know. I don't recall when last I wasn't on the Vestry.
Let's see, when we brought in a new Rector in 2001 I agreed to stay on for stability. So that would have been 1998. Almost 8 years now. And we just brought in a new Rector a couple months ago, so as Rector's Warden I should stay on for a year or two more, at least.
I think the one year hiatus rule exists to prevent any individual(s) from spending their entire lives on Vestry.