First, I can't stress enough that you really need a high-quality electric pump. I would pump 20min to a 1/2 hour or more- with a hand pump, it would take way too long to get the milk flowing and pump. I used the Playtex Embrace; the other models of that level are the Medela Pump-In-Syle and the Ameda Purely-Yours. (You are not supposed to buy them used because of HIV risk, but as a molecular biologist, I quickly realized that this is B.S., because the only parts that come in contact with milk are the cups and maybe the tubing. Just get new tubing, etc. HIV is very weak, and certainly will not survive on dry plastic for long- that's why it needs to be transmitted fluid to fluid- but you can just buy the new tubing to be safe.) One thing about the Embrace, though: it is very comfortable, but the motors have a tendency to break down, and mine did. The customer service was excellent, and they had a new motor to me the next day, but that would not be the case if you got one used.
Anyway, I would say, pump AFTER the baby has fed, when there is some milk left over (usually in the morning). Try to get her to drain one breast all the way, then go for the other, and then pump what she doesn't drink. This will also help you produce more milk. (I started pumping later, since I had a few months before going back to work, and ended up with problems producing enough milk when I went back. I was told by a stay-at-home Mom that she started pumping right away in this way, and produced so much milk she had plenty to give away.) So, in some ways, there is a silver lining to your having to go back right away- if you start pumping early, you can not only save up milk in your freezer, but you will also produce more in general, since you are "feeding" both a live baby and a pump!
Also, for when you go back to work: I found that I really needed to get into a different mode in order to produce milk. What worked for me was to make a screensaver on my PC of pictures of my baby. (In settings, go to screensaver options, and there should be an option to choose a slideshow of pictures from a folder of your choice.) I would close the office door, get the pump attached, and then start looking at the baby pictures. After a minute or so, when I started to get all Mommy-gushy at my cute little boy, the milk would start flowing! Alternatively, you could use a little photo album of physical photos. (If you don't have a private office, see if your work can provide a comfortable, private place for you to pump- i.e. not the bathroom. In some states, this is a legal requirement. A rarely-used conference room would be ideal. There are also models that work off a cigarette lighter, if you feel more comfortable pumping in your car, maybe with a light blanket covering you.)
Remember also, that if you don't produce enough milk after a few months and must use formula, keep breastfeeding and pumping- your baby will still get the good antibodies and trace elements from breast milk even if many of her calories come from formula. Good luck!!!!