It's roughly 30 minutes door-to-door, but I ticked the second option, since the Northern Line usually extends that a shade.
Short walk to Stockwell Tube station, Northern Line to London Bridge, off for a 5-10 minute walk (depending on where in the area I am temping).
I love it! I absolutely hate commuting, so I love living so close to where I work. My travelcard is £62/month on a student rate. Unfortunately, that expires in September, so it'll be the normal £89/month after that, but I get unlimited travel anywhere in central London for that.