When Nina was 6 months old I went back to work 2 days a week (16 hours) and continued to breastfeed. And when Emily was 9 months old I went back to work full time. There is another baby in the nursery room at the girls' daycare who goes full time and is still breastfed. So it can certainly be done, but the key is organisation.
You need to be organised in advance for the days you work. Each night, I pack the girls bags, bottles etc, I get my clothes ready.
With regards to expressing, this you'll need to do on an on-ongoing basis. I used to express a little each day and pop it in the freezer ready for the days I worked.