I used to time myself on the homeward journey, but my arrangements have changed - I now collect my daughter from school instead of leaving work even earlier and going home. With the old arrangement I would time my journey home (best was 18 minutes), but now I take it easy so as not to have too long to wait outside the school.
For the journey in: I try and take it easy as there's no shower facilities. So have never really tried to push it.