The effects are twofold with physical activity: It's a great reducer of stress and anxiety, and can be meditative in itself. It will also tire you out nicely toward the end of the day, or energize you in the morning (and by the time your set bed time arrives, you'll be ready for it, and need it in order to get up so early as to workout again)
It doesn't even matter what it is so much, as long as you enjoy it and are consistent: running, weights, cycling, ice skating, skateboarding, surfing, mountain biking, HIIT, or tabata-like classes, soccer, whatever else/all of the above.
I was in the same boat - solo founder, working 14 hour days, incredibly stressed. Exercise and avoiding alcohol, drugs, and shitty food is the key.
There is a certain level of stress that I think can't be dealt with. When you reach that limit, you have either step back and curtail what you're trying to do, or just push forward and get through it.
Currently I take figure skating classes, inline skate, swim, freedive, kayak, and do yoga(yin and pranayama). I might have overshot a little, as my startup (more of a side project atm) is suffering a bit ;)