I change every day at the office. I keep all my work cloths in my office, pants, shirts, belts and shoes. I take clothing for a week at a time in my panniers and leave them in my office. The reason I don't just take a change of clothing daily is that half of my commute days I'm on a bicycle. On those days I just carry underwear, socks and an undershirt in my pack.
Once a week or so I have to go straight from my office to the local Jr. College where to teach MSF. On those days it works best to wear my stich over cloths I can wear in the classroom.