Envoy does have trip trading which allows you to trade same day trips for more pay or easier commuting etc. and depending on reserve coverage it will let you switch days. It's easy to move your week day trip to a weekend but the opposite not so much. And trade a 3 day for a 4 day no problem. But almost never can you trade a 4 day to a 3 day. The nice thing is it's automated and realtime. Takes less than one second to process.