Returning Object ID and not value

I'm trying to concatenate some values for display and I have the following problem:
Given:
if (info.elapsedTime != null) {
var options = { :seconds => (info.elapsedTime / 1000) };
timer = Time.Gregorian.duration( options );
}


return timer; behaves as expected and gives duration in a 0.00 format.
return timer + " /"; returns Obj: XXXXXX /

Is this expected behavior? How can include the formatted value in a concatenate string?