15 minutes every morning would be great. Although like others have said start off every other day. Oh and do 20 minutes.
Not sure on bikes but Argos normally have some quite cheap.
RE: 20 mins on the bike in the morning. It should be noted that it should be hard work and not just a walk in the park. ;)
The Jackal
Visit Chainsaw FilmsConfucius say
"Man who go to bed with sex problem on mind,
Wake up with solution in hand"