Sri Hayagriva Jayanthi and Sri Vamana Jayanthi are celebrated during Avani Masam on Shravana nakshatra day.
For a few others, Paurnami tithi is the primary consideration to celebrate Hayagriva Jayanthi. This is based on the movement of the moon (Chandramaanam) and is celebrated in Shravana month. As a result, sometimes, this is celebrated during the month of Adi
Since there are no requirements to fast for these like it is required for Srijayanthi, Srirama Navami, Sri Nrisimha Jayanthi, usually these are celebrated by worshipping Perumal at the temple. Since no special Tiruvaradhanam is prescribed at home, one can follow the practice of the temples they visit.