The term "Prayer Watch" is especially important to Prayer Watch International because it parallels the mission's name and ministry.
"Watches" are described in the Bible. For example, in Luke 12:38, it says, "It will be good for those servants whose master finds them ready, even if he comes in the second or third watch of the night."
In Matthew 14:25, yet another "watch" is described period. "During the fourth watch of the night Jesus went out to them, walking on the lake." A companion text is found in Mark 6:48.
When PWI talks about "prayer watches," the timetable coincide with the Biblical watched as follows:
1st Watch 6:00PM to 9:00PM
2nd Watch 9:00PM to 12:00 Midnight
3rd Watch 12:00 Midnight to 3:00AM
4th Watch 3:00AM to 6:00AM
Participation in the PWI Prayer Watch is done by "watches."
That is, you sign up for one or more "watches." Each watch is three hours in length. Consequently, the minimum time to sign up for a prayer watch is three hours. Some intercessors will pray through all four watches of the night.
Sometimes Prayer Watches are offered in conjunction with Prayer Vigils.