If you're trying to lose fat from your stomach without losing any muscle, how lo!

If you're trying to lose fat from your stomach without losing any muscle, how long should you jog?

I'm lifting and getting bigger, but I heard that if you run too long you'll start losing muscle mass is this true? How long is ideal?

There's a difference between running and jogging. Jogging is easy and can go for miles and miles without much trouble. Running is what gives your muscles good tone. Instead of jogging 6 miles, run 3 relatively hard (but paced enough to make it the whole way without stopping). Run longer if you want more endurance and ability to recover, but run harder if you want more power and tone. Neither of these, unless you bs the jogging, would have you lose any muscle mass. The only way to lose muscle is to not work them; therefore, nothing else will affect them.