Stupid Subway System

I do not want this blog to become a place to rant about my personal problems, but I have to complain about the subway in NY (by the way the best system in the world). Some trains don't run all day or at night. That's fine. And usually the sign says something along the lines of "only on weekdays or only during daytime." The problem is it never defines "daytime." So I waited for 20 minutes for a train until I realized that it was no longer running. Why not just figure out the time the last train reaches the station and put it on the sign: "On weekdays until 9:26." Is that so hard or expensive?