there are a few reasons why it wasn't implemented..i think one of them was how to present such logic in a manageable way. right now we have 9 combinations(upload/download/fxp - smaller/same/larger) with 3 or 4 choices in each. now image how complicated that will become if you'll add logic for date/time for older/same/newer...that will be a total of 81-108 combinations.
if you can think of a way to present such logic to a user, feel free to share
