With my wife and I, it has been a "mood" thing for the greater part of our lifestyle. It started out as 'exciting adventures' to go out for an evening and have her get hit on and then let things progress as the evening went on. My wife would get the 'itch' about two or three weeks apart and we would plan an 'outing' on a Saturday night if the weather was good. If the weather happened to turn nasty and we hadn't gone out, she would ask if we could 'do it' some weekday instead of waiting for another week to go by.
As time went on and my wife would got her fill of cock to the degree that satisfied her, it became a once a month "conquest" as my wife called it. By then, we started sharing more time with friends and BBQ's on weekends.
But if "the mood" got to her anytime in between, she would hint in certain ways that made me realize she was getting the itch now, and wanted to spread her legs now instead of next month.
But, ....... that once a month 'conquest adventure' still happens and I find that my wife, as you might say, "let's her lover fuck her brains out" because that extra lapse of time seems to make her want to give her lover every inch of her passion to a much higher degree that in the times she was getting fucked a couple of times a month.