I don't think it varies by guide so much as it varies over time.
My guess: it's a slippery slope that slowly gets extended as guides push to make a sale. One day, 30 days is the norm, but a few guides manage to push for 60 by calling in a favor with their management. Over time, 60 becomes the norm, at which point a few guides manage to push for 90 by calling in a favor. Then that becomes the norm, and at some point the metrics show that the average delay from purchase to closing is long enough that they are no longer booking enough revenue in the current quarter, and word comes down from on high: "The Limit Is 30."
And, it starts all over again.