You have until 2 hours to transfer free between bus/bus or rail/bus AND that is only with a SmartTrip card. Mobile payments count as a SmartTrip too. However, if you transfer from a DC Circulator to Metrobus then you still have to pay the fare difference. DC Circulator ($1) vs Metrobus ($2). I think RideOn is the same price as DC Circulator so that is another one too.