I have never seen a practical application of the "50% of co-pilot time" business.
I know there's a "total aeronautical experience" field on many log books but that doesn't seem to have any practical applications these days.
An hour is an hour. A co-pilot hour takes 60 minutes to log and goes in the co-pilot column. Unless it's a single pilot aircraft but don't get me started on Caravan/Chieftain "First Officers".