I'm not so much interested in hours-per-week. I would like to ask what commitment for availability, perhaps in visits per day or time between visits, constitutes optimal moderator behavior?
There is not an official "if you're a moderator you must spend x amount of time on the stack you moderate." Moderators perform their duties at-will and on a completely voluntary basis. Which means how much time you spend on it is completely up to you.
That said, I'd suggest about 5-7 hours a week is a sufficient amount of time to budget for moderator duties on this site. Many (possibly most) moderators spend far more time on the sites they moderate. As far as visits per day? That's completely up to you. I generally have it up throughout the workday and at home during the nights and weekends and just pop over whenever I'm not doing anything else. The flag indicator appears on every page so you just have to refresh a single page to check for flags. Mods are also notified of any meta post on their site so, again, an occasional refresh will let you know if anything is happening on meta.
Different sites requires different amounts of moderator attention. I moderate the SE gardening site and it really only requires a couple hours of moderation a week (total, between all 3 of us). Other sites, (primarily the trilogy sites, and Arqade) require far more moderator time (and they have far more moderators). This site is somewhere on the busier side of the middle. There is a good reason that our election is being held for 4 moderators when a typical site leaving beta would only get 3. This site has always had a lot of flags and controversy, so much so that the initial pool of moderators was 5 instead of 3.
What I'm saying is that we need moderators who will be attentive to this site's needs. Folks who are going to show up several times a week and work for a little while, We get about 11 flags a day right now and someone has to handle those.
There are some additional guidelines, if you are away from the site for an extended period without notice, or you do not perform moderator functions for an extended period you will be asked to step down and possibly be removed as a moderator for inactivity.
So basically, the minimum you must do is log in every 3 months and perform some kind of moderator function every 6. However, if that's all one intends to do I would urge them not to run. This site has a fairly heavy flag load for a newly graduated site and there are, have been, and will continue to be situations in which we need multiple mods involved and a mod or two standing by the sidelines to step in if things get out of control.
The response from wax eagle sounds pretty on-target to me. I personally spend quite a bit more time that that on average, but it's certainly not required.
I would note that only an hour or two a week is really too little for the stage we are at. It is useful to have an extra diamond or two in a back pocket for when people sharing the normal load are unavailable (or too personally involved in a case). However at 4 mods (which is what is being elected in this round) are need is going to be for all of them to be pretty active.
While our flag volume isn't very high compared to some sites, the amount of time that needs to be invested in each one is higher than most sites. We try to do as much education as possible and even quite a bit of hand holding. This takes time to do well.
I happen to be in a fairly different time zone than the rest of the pro-tem team so I've caught a lot of flags on the times that we don't overlap. The load of things that need attention is noticeable lighter during hours when other mods are checking in periodically.
My judgement is that C.SE has a need for mods who have the availability to be active on a fairly regular basis.