You should be fine on a rode bike. My wife has had a knee replaced and rides all the time. Never any knee issues after a ride either, no matter the distance. I can tell you that the recovery period is the key to full function and range of motion later. She was religious about her pt, and pushed herself beyond to rebuild the strength and flexibility. The biggest difference seemed to be that they didn't use the "machine" to keep her knee moving after surgery. She started that day with pt and walking. She just had her five year check up and the knee was in new condition. The doctor was surprised at the things she has been doing and attributed it to how quickly she regained and surpassed full strength. Her range of motion exceeded expectations and is fully normal.
Good luck with your surgery and hope for a full and speedy recovery so you're back on the bike quickly.