4 Days a week
To me this is an improvement. Most people need a few extra hours each day to decompress from the daily grind and waste it at a bar or in front of a TV. Why not just add a few extra hours to your day and come home exhausted enough to just rest and relax. If this buys you an extra day of freedom each week I see it as a great tradeoff.
Choose wisely what you'll do on your free days and I suggest finding some time for tennis somewhere in there. If you have some other physical activity then do that but consider that tennis players tend to have better health and can stay active in their sport much longer than most. It's also a social sport so you can balance your life out in more ways than a physical activity.
Choose Tennis
