I am astonished that volunteers can be 'required' to do set hours, take fixed breaks etc! Surely the whole point of doing a job voluntarily is that you choose when you can turn up? If the person in charge is not paying you, they have no right to tell you how to organise your time.
I volunteer at the local primary school, hearing children read and giving one-to-one support to boost slow readers' progress. I liaise with their class teacher over a suitable time slot, but if I can't do it one week I just tell them I won't be available! They are very grateful and I get a lovely card from the pupils and teachers thanking me at the end of the year, in addition to the joy of watching the children blossom.
NHS U turn on trans terminology