What is a time for treadmill?
 

I think it depends on what setting you're using it at. Are you running, walking, jogging, etc? I think by listening to your body you'll know what's right. If you aren't dizzy, or in severe pain then you should be fine :) you cana always stretch before.

I used to run 60 minutes (6 miles) on the treadmill every day. After several months, I did start to burn out on account of not eating enough.

I have subsequently found a sweet spot of about 30 minutes a day, or 3 to 4 miles.

Remember, treadmills/running is good for losing weight. But cardio burns both fat and muscle. To retain or build muscle you should also be eating lots of protein and weight training depending on your goals.

What IanG said.

You'll lose some lean mass doing cardio, which means you can't eat as many calories on sedentary days if you want to keep losing. But it's a great calorie burner, and if you want a thinner look (as opposed to a lean muscular look) cardio is the way to go.

As for "too much" - listen to your body, as they say. If you're doing really strenuous running or uphill climbing, give your body a rest (especially at first) when your muscles are aching or tight after. That doesn't mean don't get on the treadmill, just take the difficulty down for a day, and do lots of stretching and healthy gentle stuff.

If you get to know your muscles slowly like that, you'll get a feeling for how far you can push yourself. Just don't injure yourself! Err on the side of caution, because if you hurt yourself you'll be out of commission for a while.