As per the Awakener Magazine, vol. 2, no. 1 (Summer 1954), p. 34

“Baba desires all those who love him to:

1) Observe fast and complete silence from 5 A.M. on July 10th, 1954, to 5 A.M. on July 11th, 1954 (Eastern Standard Time, U.S.A.).

2) To try to keep pure in thoughts and actions during this period of silence.

3) To repeat inwardly any one Name of God as frequently as possible during the 24 hours of fast and silence.

During this period of fast, tea or coffee is permitted thrice. Drinking water may be freely taken.”

However in 1958 Baba made changes to the above said that:

“This time no one should keep fast or silence but repeat seven times in a just audible voice (not shout) exactly at midnight between the 9th and 10th of July according to your local time: ‘BELOVED GOD, THY WILL HAS COME TO PASS.’” —The Awakener Magazine, vol. 5, no. 3 (1958), p. 36

For 1956-1968 Baba’s wishes for the observance are documented in 82 Family Letters by Mani S. Irani, a collection of letters sent out to group heads in the West (these letters began, by Baba’s direction, after his 1956 visit to the West). Mani mentions Baba’s wish for the observance of Silence Day in the years 1963-1968 (see Mani S. Irani, Family Letters, pp. 167, 198, 225, 258, 281, 320). For example:

“On the 10th of July 1967, the 42nd Anniversary of His Silence, Avatar Meher Baba wishes all who love Him and all who would want to do so, to observe Silence for 24 hours.”

Bal Natu wrote in his biography of Meher Baba:

“Meher Baba had begun observing silence on July 10, 1925, and His silence remained unbroken for over forty-three years, until He put aside His Man-form on January 31, 1969. From 1953 onwards, almost every year, a circular was issued at Baba’s direction giving specific instructions to be followed by His lovers on Silence Day, if they wished to do so. Sometimes He asked them to repeat a name of God, audibly or inaudibly, other times He wanted them to fast or keep silence, or both. In the last circular of its kind, issued by Adi K. Irani in May 1968, Avatar Meher Baba expressed His wish as follows:

On the 10th of July, the 43rd anniversary of My Silence, I want all My lovers to observe complete silence for twenty-four hours, from midnight of 9th July to midnight of 10th July 1968.

“Adi, Baba’s secretary, added the following lines:

Please note that Baba has given no option of a fast for those who may find it impractical to observe silence. None must write for further clarification (to Baba) concerning it. [Life Circular, No. 69, May 15, 1968]

“This was the last time that Baba gave a specific instruction to His lovers about July 10. Now that the Avataric “cloak” (the physical form that Infinite God put on to become Meher Baba) is removed from our sight, it is natural for some to ask the mandali whether or not silence should be observed on this particular day. In 1979 Mani, Meher Baba’s sister, shared some of her thoughts in an informal talk on this subject in Mandali Hall at Meherazad. She said:

‘There should be no question in the minds of anyone [Baba lovers], whether we should observe silence or not. It is an opportunity that we should not let pass by! Every lover of Baba, to my mind, should observe silence on the 10th of July — Silence Day. You salute your Beloved Baba by giving Him a rose; you would not call that a routine or ritual. It is an expression of your love, a piece of your heart . . . Baba has observed silence for all — for each one of us — and if we cannot give that little response for one day — if we cannot keep our lips closed for one day of the year — then that’s too bad. I don’t feel that by keeping silence we are going to help the world or anything like that. That is not why we are doing it. It’s just a salute, in homage to His Love for us; an expression of our love for Him. Beloved Baba observed silence for all these years, and for one day He has “said” we can share it with Him too. How blessed we are!’

– See more at: http://trustmeher.org/meher-baba-news-archive/meher-baba-silence-day-july-10.php#sthash.sWIDdCIN.dpuf