Look - we all know everyone needs a release for their stress. What really used to stress me out when i was a kid was when my uncle used to sit on my chest and blow into my nose.
And think about it - nuns are typically women, so they are empty inside according to the WT - plus they're Catholic - so they already got two strikes against them when they step up to the plate. Trying to put a restriction on their masturbatory privileges will just make them feel paralyzed and will lead to greater problems.
I think the real focus should be on 'drunk women'. When you have a masturbation exacerbation problem - the nuns are just going to turn to alcohol and that will ruin it for the rest of us because there is nothing worse than a drunk nun (or woman for that matter) in a pub. They get really loud and high pitched screechy sounding like minnie mouse. I say let the nuns masturbate.