It is as much work (play!
) as you want it to be.
I started with a 48 site category. I probably had 3 or 4 editing sessions lasting around 2 hours each the first week. I spent that time getting the hang of the editing interface, re-reviewing listed sites and starting to clear out the unreviewed. I probably spent 8 or 10 hours the second week hunting new sites. That was about when I realized how extensive the editing community was and how much knowledge was in the forums. The next couple of weeks I pretty much stopped editing and read a lot of the forums - lunchtimes just flew by!
After that I edited around 5 hours a week, adding sites I'd found. It took me 10-30 minutes to review them, mostly because they we interesting to me and I kept getting distracted.
After 6 months I had the category to 250 sites and decided to get a 2nd category editing my hometown. That was when the editing bug bit and I really started spending time editing.
Been addicted ever since.
As far as time commitment goes, I would say you need to plan to spend 4 or 5 editing sessions of 1 to 3 hours each in order to get started and really start digging into the meat of what editing is all about. Exactly what you do and how many sites you edit will depend a lot on the category you edit in.
Just a different perspective.
<added>
I'm sure a lot of folk reading are thinking - 10 hours a week, you've got to be kidding! Well, I don't watch TV anymore in the evenings - that's an easy 2 hours a night I spend glued to my monitor instead of glued to the boob tube. Lunchtime provides 5 good hours of editing opportunity and a mental break. And often I squeeze in an afternoon session on a weekend day (yeah naptime!) Now if only I could edit while I'm carpooling to work ...
But don't get me wrong - if you only want to spend 1 or 2 hours every couple of months, that is wonderful too.
Every little bit counts!