Firstly, let me make it clear that any time of the day is better than never. So if you find yourself unable to set time for your rehab exercises when it might be the most ideal, you're still reaping the benefits by doing them whenever else you can.
As for when the most ideal time is, my opinion is that performing them as closely before the most physically-active time (or times) of your day is the best. Whether you're doing it as part of your warm up before working out or before leaving for work at a labour-intensive (or even a low-intensity) job, rehabbing prior to other activity will likely see the most benefit.
After all, the point of rehab is to create a change in the way that you're moving to eliminate and prevent pain. Practicing those new ways of movement before other activity or tasks is going to provide an opportunity to let those exercises carry forward in the day. Essentially, you get to practice using those new mechanics throughout your daily/workout routine.
In contrast, simply going through your entire day or workout first and saving your exercises until the end might mean you've just spent all that time reaffirming your old ways of movement.
As I said, if early doesn't work for you, I understand. It's not realistic for every client who works at 6:00AM to set aside an additional 20 minutes in the morning to exercise before leaving for the job site. (Although I always do expect my athletic or gym-going clients to incorporate it into their warm ups for best effect.) But all in all, as long as you do them at all, I'm happy.