It is generally very helpful for them to know that every Monday night from 11-11:30PM (PT) and every Thursday night at the same time, our API’s will return an ERR_IN_SERVICE response (and part of our return XML suggests a next retry time in minutes 10).

Our UI provides them with the equivalent (though friendlier) message.

With two maintenance windows per week, it gives us an opportunity to release often enough to satisfy most customer requirements for features and fixes.

With a half-hour service window, we chunk up functionality so that it can be deployed and verified in that time span.

(On rare occasion, we need to release a larger build. Then we call [with at least a week's notice to customers] for a longer maintenance window on Saturday night.)

I appreciate your attempt to analogize application releases to Seth’s example of ad spend, but (as you can no doubt tell from the gist of my comment), I don’t think the analogy holds.