Neat quote from "Dragnet." From my observation, most Catholic churches in Midtown Manhattan today are open all day from about 6 a.m. till at least 6 or 7 p.m., regardless of whether Mass is being said.
Maybe it's because in Midtown, the daytime population is so big that there are almost always people praying in any given church. The Catholic custom is that it's good to visit every day for a time, to keep Our Lord company. It may have the unconscious effect of discouraging crime for at least half the hours of the day.
Many's the time our parents/aunts/uncles would make a quick stop when passing the church. My sister always tells a funny story about when she was little and our aunt would often babysit her for our mother. The aunt could hardly pass a Catholic church without stopping in for a few minutes. And because girls were supposed to wear something on their heads in those days, the aunt would pull out a dirty Kleenex from her purse and bobby-pin it to my sister's hair before going into the church. You should hear my sister tell the story. It's a great story, though sadly I think that that memory is one of the things that drove my sister away from the church.