D.W.
I had to start pumping with both kids when going back to work as well. It sounds like your daughter is a nurse (based upon the shift work and unpredictable schedule). I was fortunate to have time available during the day to pump (had to do it in my car as a travelling sales person). However, I usually only pumped 2-3 times, and I was able to keep my production up very well based upon demand.
That's the most important thing - demand will create production. So, my advice would be to pump as soon as she wakes-up and then have the baby nurse when he wakes. I'd then pump mid-morning, after lunch, and on my way home (around 4:30-5pm). I'd nurse until after he went to sleep and would pump again at 11-11:30pm. I intentionally did this much to overproduce what he needed.
As great as breastfeeding is for the baby, her schedule may wreak havoc on her ability to produce a consistent amount. With my first child, I was so adamant about nursing for the first year. Then, not quite 3 months into my second child, I was diagnosed with cancer and had to stop nursing. I learned that formula wasn't as bad as I had it in my mind.
So, my advice would be to try to make it work, and if it doesn't, nurse when possible, pump as much as you can and supplement if needed with formula until he's ready to start solids in a few months.
Good luck to you all!