I think opnot left a day out. Should be mmaannsooo. The two night duties can also be rostered as 2 day duties.
Personally, I never found the system tiring. Four days off on the trot was enough R&R and the mornings and afternoons gave you half a day "free" at home. Loved it... The old 4-watch was the nightmare - afternoon first day, morning AND night second day, sleep day, day off... back to afternoon, etc.