martin j wrote:
Got to get to Harrow on the Hill, Tuesday evening and Journey Planner
says 12 mins for the Met Line from Finchley Road to Harrow on the
Hill.

Met "main line" timetable says 13 minutes. You can find said timetable
he
http://www.tfl.gov.uk/assets/downloads/first-last-amersham-northbound.pdf

Cheers,

Barry