Don't do overtime unless you are paid for it!!! Remind them that "Flexability does not mean getting postmen and women to work more hours than they are paid for."
unless you have a local agreement stating otherwise your delivery span should not be over 3.5 hours. Ask in writing to have your duty tested by agreed procedures (not pegasus there is no national agreement on its use). You do not have to work any more than 3.5 hours on the street and they can't make you!
I know thats much easier said than done.
if you feel your are being harrassed (which you already are being, ask for a bullying and harrassment form)
if they blame your performance ask for training help. problems with performance requier corrective action not disaplinary (think thats RM and CWU policy)
if all else fails resort to threats.
ie. do your managers sign in and out, there supposed to for the fire redgister H&S policy, They don't in our office, managers like to leave early when they can, usually on a Saturday. THEY ARE NOT ALLOWED TO DO THIS! EVEN WHEN WE HAD A JOB AND FINISH THEY DIDN'T! THIS IS BREECH OF CONTRACT! I've asked two DOMS and a DSM about this they were all coy and had diffrent answers. Made a fuss about this when i was getting signed late for one or two mins. I've since been late by more than an hour and told not to bother signing late. managers are s**t scared of this. Bring it up at WTL session mention the fire redgester.
ps. not advising you to carry out a threat of going above their head about this just subtely make it at WTL.