Four men — Jake, Deon, Fred, and Eddie — are watchmen in a small factory in Lorain. Their job consists of two daily shifts of six hours each, interrupted by a rest of several hours. At any hour of the day or night there must always be two men on duty. However, no two men's shifts may end at the same time — it is not wise for both people on duty to begin their shifts simultaneously. Each shift has to begin on the hour. Except for these rules, the four men may agree among themselves on any schedule they want.
So they have a meeting at which they ask for the following privileges: Jake wants to start his first shift at midnight and would like to be off for the day by 4 pm. Fred wants to relieve Deon after Deon's evening shift. Eddie has to be on the premises at 9 am to receive special instructions.
After some trial and error the four watchmen finally succeed at making out a shift schedule in accord with the regulations as well as their special wishes. What is the schedule?
Source: More Math Teasers (1973)