I wonder if this method should use `self.replicate()` instead of `self.copy()`.  That will make a new version that just uses a reference to the original internal JD values.  This is OK because Time objects are immutable.  I think of `copy.copy` being a lightweight, reference-only copy. 

Having said that, the existing code here does work, and in a possibly-imperfect world doing a deep copy here may be safer.