The dates of shape note singings are determined by counting Sundays. For example, the Georgia State Sacred Harp Convention is held "the fourth Sunday in March and the Saturday before." This system works well for scheduling and coordinating annual singings, but of course the dates change from year to year. In the fourth Sunday in March and the Saturday before is the weekend of March .
(FAQ: "Could someone please let me know if the Georgia State Convention still happens when it falls on Easter weekend ?" Answer: Yes, it is held on the usual weekend, Easter or not.)