This feature already exists in OmniFocus 1.7.5, but it is disabled by default. You can turn it on with a hidden preference setting. Paste this into Terminal and relaunch OmniFocus.
Code:
defaults write com.omnigroup.OmniFocus RelativeDateFormatterShowTime YES
I've been using this for months and it works quite well. But if you don't like it, it's easy to return to the default behavior with this command:
Code:
defaults delete com.omnigroup.OmniFocus RelativeDateFormatterShowTime
-Dennis