Never heard of that either and by the way why only 3 - 4/week?:)
There is something I read a while ago like
1- They should fulfill each others needs.
2- Not being able to fulfill the needs of the partner can be a ground for divorce/Khula.
3- They should not stay apart for a long time. (Anyone can correctme but Umer (RAA) made some rules for those men on battle far away to come home about every three months based upon a woman's inquiry and question)