Hi,

I think I know what is the root cause of this :) Look at this line: https://github.com/ReactiveMongo/ReactiveMongo/blob/master/bson/src/main/scala/typeclasses.scala#L69-71

The `BSONNumberLike` type class should handle all BSON numeric types, including `BSONDateTime`.  I just saw that there is some problem with `BSONDateTimeNumberLikeClass`; I will merge this pull request then fix this problem also :)