I have created a helper for working with MapSet.

import MapSetEx
now = DateTime.utc_now()

checker = fn 
  mapset when is_empty_mapset(mapset) -> :empty_mapset
  mapset when mapset_size(mapset) == 3 -> :mapset_with_three_elements
  mapset([^now]) -> :now_mapset
  %MapSet{} -> :mapset 
  _ -> :unknown
end

checker.(MapSet.new([]))
#⇒      :empty_mapset
checker.(mapset([now]))
#⇒      :now_mapset

Gist: https://gist.github.com/am-kantox/03325197ff9608dfa83457dbe0d144e9