Route 9 never really sleeps, but there is an hour near two in the morning when the storm has the whole corridor to itself — snow sliding across four empty lanes, the Speen Street lights swinging in the wind. That is Cross Services Group, Inc.'s hour. Plows push the lots and drives back to their true edges, walks get cleared down to the concrete, and treatment goes where the melt will run and refreeze before sunrise. Nobody sees the work; what they see is a clear approach and a door they can reach without thinking about it. From Natick the routes carry out into Framingham, Wellesley, Ashland and Wayland, storm by storm, all winter long.