No no no... the test for session expiration is business logic and absolutely does not belong in an implicit. Do not pimp anything onto a third party library object if it couldn't reasonably have been added to the library in the first place. i.e. would the implementer of JodaTime reasonably consider releasing a version of JodaTime with our custom implementation Play framework cookie session expiration test on `DateTime`?

The key element of implementing the logic you want is knowing how old the `lastSeen` `DateTime` object is. There is nothing Play Framework or cookie session expiration specific about asking a `DateTime` object how old it is. Nobody would shoot the JodaTime library maintainer for putting an `age()` method on `DateTime`. This is the bit of boilerplate/clutter that you want to remove to the implicit. 

Put an `age()` method on `DateTime` in an implicit in `implicits.Dates` please.