That one example does not sufficiently describe the rules for combining  
the two values.

You certainly can take the Date property from one DateTime and add it to  
the TimeOfDay property from another DateTime.  That's simple enough and in  
the very specific example you provided, it would produce the output you  
describe.

But is that really what you want to do?  If so, why are you using a  
DateTime for the second value in the first place?  Why not just a TimeSpan  
to start with?

Pete