There are twenty-four hours in one day, and thirty (or thirty-one, whatever you want) days in one month.
So:
24 (hours) x 30 (days in one month) = 720 (hours in one month)
720 (hours in one month) x 9 (months) = 6, 480 (hours in nine months)
No, 1,500 hours does *not* equal 9 months.