Work hours in a week?

I work as a porter/maintenace within the univercity.I would like to know if my shifts are legal.I start at 4pm till midnight then i go on call through the night a have to get up to deal with problems.At 8am i have to do the day shift till 4pm.Thats a 24hr shift.It work out including the nights that i am there 60hrs a week and get paid for 40 as they do not pay me for the night........is this legal...