About two minutes, it seems like the longer puzzles provide more clues than a short pithy one.
Claude Shannon would agree. Shannon, the inventor of information theory, wrote a classified paper in 1945 on cryptography. Shannon coined the term, "unicity distance" to denote the amount text one needs in a cipher message to unambiguously reconstruct the plain text. For a monoalphabetic substitution cipher (like a these) in English, it's about 25 characters, on average, without any gimmes like spaces or punctuation. Spaces and punctuation make it easier.
Use of a one-time pad sets the distance to infinity. The code is unbreakable. What is surprising is that reuse of a one-time pad reduces the unicity distance to about 15 characters(!). The Venona decrypts were only possible because the Russians reused one-time pads, making them some-time pads. Even one reuse defeats the purpose. They must have been hoping that the Americans were not paying attention.