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How much time....the million dollar question.
The real answer is how much do you want to give. The minimum editing requirements to keep a password active would probably amount to 15 minutes every three months. Anything you want to contibute above that is welcome, and the only real pressure you will feel in terms of wanting more, will be from within.
No one can make you contribute mroe time than you are willing to give -- and our attitude is that if you only do six edits a year, that is six edits that someone else wil not need to do. And, since there is no concept of slots or staffing requirements, or headcount -- even if you do only the bare minimum in terms of edits, you are not taking up space and you are not keeping anyone else from editing.