What's the Difference Between Nine First Fridays and Five First Saturdays?

 Both are devotions.  Both involve attending Mass and receiving Communion.

How do they differ:

The Jesuits are in charge of promoting the Sacred Heart of Jesus. The devotion was requested by Jesus in a vision to St. Margaret Mary Alocoque (1647-1690).  She was a nun in the Visitation Order.  I think maybe Father Claude de la Colombiere, sj was her spiritual director.  Anyway, he helped Margaret Mary promote the devotion.

The Saturday devotion was part of the message when Our Lady appeared at Fatima in 1917.

She said to Lucia, the oldest of the three children:

“I shall come to ask . . . that on the First Saturday of every month, Communions of reparation be made in atonement for the sins of the world.”

Years later she repeated her request to Sr. Lucia, the only one still living of the three young Fatima seers, while she was a postulant sister living in a convent in Spain:.

You can find more information at this link: https://www.catholiccompany.com/magazine/what-is-the-first-friday-and-first-saturday-devotion-5781