12 hours works me no problem.
The shift are min of 3 hrs. you can be send home after 3 hrs. Max is 8 hrs unless you are asked to stay OT. Hrs are not guarantee. The casual staff waits for the call each morning no schedule all base on sonority, term position, calls, advancement to full time or part time are base on sonority. Shift are 99% night time, remember mail gets picked up during the day, sorting occurs at night.
I stayed part time for many years and had the option of working more hours. So I was flexible and so were they.
The three shifts are: 11pm -7am, 7am - 3pm and 3pm - 11pm. The overnight shift is very busy during Christmas.