No, hours are not really that closely linked with firm prestige. The truth is, a lot of the top firms are more profitable because they do work that commands a higher hourly rate. For instance, antitrust rather than employment law in litigation. A lot of times, its the lower ranked firms that have billables requirements. Dewey Ballantine does, Simpson Thacher and Davis Polk do not. Cadwalader will have killer hours, arguably moreso than a lot of V10 firms. I am actually of the opinion that unless you are picking a firm based on a niche practice, you should only go about 10 spots lower down on the vault than your highest ranked firm, unless you really hate that firm. The quality of life will not be different and you will be happy to have the exit opportunities.