Just to concur with Inov 8, as someone who hasn't run since the end of March I have just been out for the 2nd successive day for less than 30 mins steady jogging. My legs did ache on this 2nd day but as someone who adopted the same philosophy as yourself Mossdog up until a couple of years ago I am now convinced that a 20 minute blast is just as effective training wise compared to plodding for 90 minutes or so.