Eden, I found that the longer I wear them, the better I feel the next day. But, sometimes, I don't have time to wear them for more than a couple of hours. And despite that lovely picture of Susan O. and her friends wearing the Zoot tights after a triathalon, I don't think I want to run around town in my compression tights (plus, I think they might be a tad hot).
I also would be interested in reading a study that discusses benefits/length of wearing, etc.