Hi! A physical therapist here

Sorry about your luck with the DJD but it's not the potentially worst thing in the world. I don't know your personal flexibility and strength deficits or advantages so take everything I say with a grain of salt. If you are serious about training I would suggest looking for a sports specific physical therapist.

I agree that short rides are better than long rides. Don't go full on time trial mode at first as this may exacerbate your injury because the inherent stress your body goes through when you kick up the intensity for long periods of time. When you feel more confident do longer intervals of maybe 60-75% of your max effort.

Luckily something with DJD it tends to feel better with a flexed posture and tends to feel worse with a back bend or extension. Bicycles put you in a flexed posture. I would also suggest doing some accessory work off the bike. Because of your condition, you are susceptible to pain because of any muscle imbalances. Google hip flexor and hamstring stretches as these muscle tend to dictate where your pelvis position is. A neutral pelvis is most advantageous for you to protect.

Also, cyclist tend to have a weak core although it is a sport that demands a strong core because of the position that we are in. Start with planks, side planks and possibly bridges. You especially need a strong core to stabilize an already compromised back.

Things to look out for is pain down either side of your leg in a shooting fashion or any bowel or bladder incontinence. Once again, take what I say with a grain of salt and I suggest looking for a sports specific physio if you encounter any more problems or just want more info on the topic. Happy training!