7 km, roughly, one way. Takes 20 minutes on touring bikes, 25-30 on comfort hybrid. I ride mainly on the road, but have to dismount several times in order to cross railway tracks and other obstacles.
I would recommend doing a test ride on a day you are not working to see how long it takes you - no time pressure. Also, carry what you normally take to work. First time I commuted was on beater mountain bike, after I missed the bus and was determined not to be late for work. It was not, shall we say, enjoyable.