Saheeh Bukhari Volume 7, Book 71, Number 601:
RECOMMENDED TIMES TO DO HIJAMA:
Anas bin Malik (RA) stated the Prophet (PBUH) used the treatment of cupping on both sides of his blessed head and shoulders and generally this treatment was done on the 17th, 19th and 21st of the Islamic lunar month. (Tirmidhi).
It is best to avoid Wednesdays and Saturdays for Cupping as recommended.