April 7

Regarding your questions: the Devotional part of the Nineteen Day Feast means the reading of prayers by Bahá'u'lláh and the Master. If, after this, there is a period of reading of the teachings, his [the Guardian's] writings may be included, but this does not form part of the devotional aspect of the meeting.  
- Shoghi Effendi  (From a letter written on behalf of Shoghi Effendi, 15 December 1947 to an individual believer) The Compilation of Compilations, vol. I, Nineteen Day Feast)