https://infogalactic.com/info/Prime_(liturgy)
> Prime, or the First Hour, is a fixed time of prayer of the traditional Divine Office (Canonical Hours), said at the first hour of daylight (approximately 7:00 a.m.), between the morning Hour of Lauds and the 9 a.m. Hour of Terce. It is part of the Christian liturgies of Eastern Christianity, but in the Latin Rite it was suppressed by the liturgical reforms following the Second Vatican Council.[1]
> As the chronology of Cassian's works has recently been established fairly accurately, the institution of Prime must be placed towards 382.[4]
So from 382-1960s (?) this was observed but the Vatican 2 church broke from this tradition....
> "Seven times a day I have given praise to thee, for the judgments of thy justice." Psalm 118:164
Jewish custom was prayer seven times a day? The Divine Office Was 8 times a day: Matins, Lauds, Prime, Terce, Sexta, Nona, Vespers, Compline. By removing Prime, it makes it seven. I don't know if this was to be more "ecumenical" and like Jewish practice, but this came to mind.