Take a 101 Stagecoach Bus @ 11:20 from Edinburgh Bus Station for a 12:30 start from The Allan Ramsay Tavern, Carlops. (You can also catch the bus at Princes Street, Lothian Road, Tollcross and Morningside).
Then over the Pentlands to Balerno. About 4 hours walking and half that running. No climbing up the top of the big hills.
44 Lothian bus back to the West End / Princess Street.