Originally Posted by BlazingPedals

I think you mean you'll be switching between a (upright) bike and a (recumbent) trike. Not that the adaptation issue is any different, but it's important to note that not all recumbents are trikes. With 'bents, there is a tendancy to mash more, because it's an easy trap to wedge yourself between the seat back and the pedals, and just push. "Seated squats" so to speak. The adaptation is mostly about using generally the same muscles in slightly different ways in order to smooth out the pedal circle somewhat. How long it takes sort of depends on your standards of performance; it might take you longer if you have higher expectations. For most people, they will feel comfortable within 500-700 miles.