Nicholas V, in 1450, reverted to the quinquagesimal period, while.    From Wordnik.com.  [The Catholic Encyclopedia, Volume 8: Infamy-Lapparent] Reference

Hence the time of our sorrow and affliction is fixed at forty days; the state of blessed joy which shall be hereafter is figured in the quinquagesimal festival, i.e. the fifty days from Easter to Pentecost.    From Wordnik.com.  [Catena Aurea - Gospel of Matthew] Reference