I just had a thought Dave36... I may be odd, but if my H suggested "ML or sexual play every 3 days minimum", I'd feel a bit obligated. Would your chances increase at all if you were to suggest it more subtly like, "ML or sexual play a few times a week"? Maybe once (at least on weekends) and once (at least) during the week... it pretty much turns out to be every 3 days.
There's just so much pressure when a set schedule is requested. If your approach is more subtle, she may surprise you with more frequency.