Welcome to the site, Zeke and here's something you may not like - you need to be patient.
Once I got going, I wasn't just sitting around (which is painful early on), but I definitely got house fever. So you're doing home PT with a therapist, so you have your group of exercises. Right now, you should be giving those insulted muscles and bones all the support possible. Ice, elevate and move - you're doing right with the exercises, I assume you're doing walking on that walker and plenty of sleep as possible.
As to the cardio, etc - first and always check with your surgeon, they all have different restrictions, and even per each person, there are different challenges - are you 100% weight bearing?
I didn't ride a bike until I started outpatient PT at four weeks out, when I went on a spinning bike for 10 minutes (no resistance) about every other day. The seat hurt at first, but we took care of that quickly. I would think more strengthening the hips, working on your gait and making sure your body is being fed well.
I didn't think of aerobic workouts until at least three months out. Other folks may be different, but that was my pace. I think most surgeons also put a limit on what you lift until certain amount of time goes by. Your body is still healing and the bone is still attaching itself to your device, so this early, whatever you can do to help that is much more important. The cardio comes in time.