To add a new favorite place (for any location, not just home or work!):
Open Cortana > Open her Notebook (three lines in the upper right corner) > places > '+' sign > Type address and/or search for an address > Tap result you want > Finally, save as 'home,' 'work' or 'other.' You can give the location a custom nickname for any of these!
Unfortunately, at this time: You cannot customize when Cortana suggests you leave for work and when she suggests you head home (at least that I know of). Maybe a future update, but alas: Not at this time.