I am replying to this query based on the assumption that you have undergone Vedic studies. Dharmasastras had provided elaborate details on this.
The period of study is called Adhyayana kalam.
Pournami, Amavasyai, Ashtami, Chaturdasi, and Prathamai are Anaddyayana days. During these days, one should not learn Vedas and recite them in Sandhai.
Divya Prabandham and Stotra patam can be recited during Ashtami and Chaturdasi. Sandhai will not be conducted during Ammvasyai, Pournami, and Prathamai but parayanam is allowed.
Anandhyayana kalam consists of many other specialties.
There are many calculations for Vedic Anandhyayana kalam like the Nazhigais of Ashtami or Pournami, etc. We shall look into this in detail at a later time.