It's not voluntary. You are hounded to death to go out in field circus, and then you are hounded to commit yourself to putting 50 hours a month in field circus. Then, if you don't make your time, you are in for a hounding from Brother Hounder. They will make it look like you are a total failure if you do not get all 50 hours you promised.
Then, why not just do the time? You could just do the 50 hours, but then they will start hounding you to commit. If you fluctuate just under 50 hours, they will start hounding you to commit--even if you are above and below 50. You could be doing an average of 50 hours a month, with some months of getting 55 and others 45 (and it's impossible to tell where you will be until well into the month). What they want is to force you to get in those extra 5 hours during a "short hour" month, at possibly great hardship to yourself.
Voluntary? Huh.