Replying to FCP timelapse question

i ran into a problem trying a timelapse in FCP today. i filmed a sunset so i had about 30 minutes of footage that needed to be sped up to about 3 seconds. this means the footage needs to be 600x shorter than its original length. however the "change speed" option in FCP only lets you speed footage up by 100x. Even after the sequence change is rendered, the previous information is still held, so you can't speed it up again. There has to be a way around this...does anyone know?