Personally, as a newbie to the mod, I feel that monthly is way too slow. I spend most of my time in Custom Settlements sitting around trying to pass away (as opposed to piss away) the time. I'd be happier if it gave a weekly benefit, but provided 1/4th the actual output: this way it actually feels like they're doing something, even if the rate is the same. It also lets you get a feel for what adding a single jack or jill does to the production rate.
Better yet, daily, with 1/30th the actual output. (How well does M&B handle floating point, anyway?)