Period of nighttime prayer (5)
I believe the answer is:
vigil
'period of nighttime prayer' is the definition.
This is the entire clue.
(Other definitions for vigil that I've seen before include "Through the night, one kept" , "The rite of staying awake for devotional purposes" , "A period of staying awake as for prayer" , "Peaceful demonstration" , "Rite of staying awake for prayer on the eve of a religious festival" .)