The process requires adequate temp for at least 3 months. The key to dark color is the number of times you pull it all out, expose it to air, then re-moisten and re-press. The O[sub]2[/sub] in the air oxidizes the nicotine that has been squeezed out of the ruptured cells. So, my take is that time alone won't darken the leaf as much as repeated exposure to air (like at least a few times, during the entire processing period).
Bob
Bob