It is necessary to carefully distinguish between the times when you would like to receive shift offers and your availability (or unavailability). For example, a shift offer goes out on Sunday for a shift that is to be worked the next day (Monday).
Unavailability: You might notify your portfolio clerk that you are unavailable to work on Monday. You would not be contacted for the Monday shift because you are unavailable on the day to be worked.
Contact Preference: You might set your contact preferences such that you are never to be contacted on Sunday. You will not be contacted for the Monday shift because you have indicated that you do not want to receive any shift offers sent out on a Sunday.