1) Blood moons (and darkening sun) in the bible sometimes mean something according to prophecy and
2) Israel uses God's calendar, or perhaps a modified derivative thereof, to at least keep the feasts going and remembered, something that without the Jew the world would have long ago forgotten in favor of other calendars, namely, Gregorian solar.
The "set times" of the Lord is using the sun, moon and stars like giant clock hands. When they are in such-and-such a postion, there is a feast. We don't find it odd if we make appointments, such as a doctor's appointment. Maybe a kid notices each time he gets sick, when the clock hands are facing upward, he goes to the doctor (say, near lunchtime). He gets sick again, but this time the parent may schedule it for another time, but the kid has every right to associate and speculate what may happen when the clock hands are upward, the same way with tetrads as based on the past.