im on a 25hr contract though i have one of the largest duties in the office.
i found out the hard way and after a couple of years of it i did cut off on a day that suited me, the office had all duties covered and i left my last bag in the frame told DOM and left the building.
an hour later both managers turned up in a van with the bag of mail and put me under extreme presure to deliver it, i was very upset and foolishly agreed to take it.
that evening i sat a wrote a diary of the day and next day i presented it to the CWU rep and told him i wanted to report the DOM for B&H.
this was over a year ago and though the CWU bottled it after confronting the manager i put it down on the next have your say questionaire (no doubt the manager knew exactly who had writen it) but i now cut off whenever i need to.
i helped out with OT over the xmas period 2010 and as im sure you are aware jan 2011 has been even heavier but im now cutting off regularly and the managers are having to take the mail out
make sure all your indoor work is complete then decide where you finish and leave the mail.
all the best, jonny.