Hi Jacqueline, your schedule sounds really challenging. I know from my long days that the last thing I felt like doing sometimes was exercising...just another chore to put into the day. Now I look forward to it and just don't feel right if I don't do it.
My thought would be to start slowly and build yourself into it. Just like making small changes with food, do so with working out also. For example, pick 3 days and do 15 minutes in the morning and 15 at night. As the weeks go by, you could add in days and then gradually extend the time. There are some AM/PM yoga dvds out there that you may want to check out.
What works for me is to print out a blank calendar every month, look at my workload and other activities for the upcoming week (some days are busier than others), then plan out what exercise to do each day and for how long, usually working around how busy the day is or how tired I think I'll be. I put the exercises in the blank spaces for the days and stick it on the fridge, and I do it in pencil so I can change if something comes up. They say if you schedule it, you're more likely to do it.
I know it is hard and you have a brutal schedule. But if you can do it long enough to develop the habit, you won't look back!
And now that you don't have to be perfect, you can be good.