For clarification, Red Alerts happen 3-5 hours after the last. The exact difference in respawn time seems to be random. So it's similar to the hunt (A rank) respawn times.

Mech Ops seem to respawn about as often as FATEs, which is within 20 minutes.

I agree that I have been getting I and II research from Red Alerts. And there is no skill needed for Red Alerts so far, at least for gatherers. They aren't nearly as challenging as the steller missions. So if you just want to tab out and only do Red Alerts when they come up, it seems to be workable so far.