Word Problems with Quadratic Inequalities

A skydiver jumps out of a helicopter 2500 meters above the ground. For him to land safely on the target below, he has to open his parachute between 1500 m and 1000 m above the ground. Ignoring air resistance his decent is modeled by the equation $h=2500-5t^2$ where $t$ is in seconds. Rounded to the nearest second, what is the time frame that the skydiver has to safely open his parachute?