The following songs from my iTunes music library have a length of exactly 4:20.
- Peaceful Easy Feeling (The Eagles)
- Smokin’ (Boston)
- Don’t you forget about me (Simple Minds)
- Goodbye (Alicia Keys)
- Solsbury Hill (Peter Gabriel)
- I’ve got friends in low places (Garth Brooks)
Obviously, “Smokin’” by Boston is 4:20 in length on purpose. I also suspect the same for “I’ve got friends in low places” since it contains the lyric “I’ll be as high as that ivory tower/That you’re living in”. I think the rest (save for maybe “Solsbury Hill”) can be chalked up to coincidence.