March 5

He would like to point out that if the believers gather before sundown on a certain date it does not matter if the meeting continues after sunset; it may still be considered as being held on the day they gathered. The Naw-Ruz Feast should be held on March 21 before sunset and has nothing to do with the 19-Day Feast. The 19-Day Feast is administrative in, function whereas the Naw-Ruz is our New Year, a Feast of hospitality and rejoicing. 
(From a letter written on behalf of the Guardian to the National Spiritual Assembly of the United States, July 5, 1950; compilation: Lights of Guidance)