I've tried it with 1-5 minutes and 1-60 seconds, but it still keeps dropping on the same spot in 2 of my monuments.

{
  "Don't drop above water": true,
  "Don't drop above structures": true,
  "Minimum time until drop (in seconds)": 1,
  "Maximum time until drop (in seconds)": 60
}​

Is this still an issue? After the rework of the crate dropping check this should not happen nearly as often anymore, though it is still very possible for the chinook to drop its crate on its own volition before this plugin tells it to drop its cargo.