Im a boy. if i masturbate 3times in a row each of gap 5-10mins. i finish within 3 mins for first 2times and last more than 25mins on last one. why is it so? is it any good indication or bad? is it premature ejaculation? or does this leads to it?

You are masturbating too much. The results you described are what would be expected. Masturbation does not cause premature ejaculation or any other disease. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.

You have 'emptied' out the secretions the first two times so the third time it will take longer to ejaculate and it might be less in volume. It is not premature ejaculation and does not lead to it. I would suggest to temper the frequency if you can and stop timing yourself.