You need to use the TIME L

You need to use the TIME LAPSE record settings on the FS100 itself, not the time lapse feature on your camera. Set everything up as your normally would to shoot HD, and then go into your RECORD screen on the FS100. Scroll down to TIME LAPSE, and the set the intervals in hours, minutes, seconds and frames. Then hit record. Wait a few intervals and check the timecode on your FS100 to make sure the frame counter is incrementing upwards. If it’s counting up, you’re good to go.

EDIT… I should note that this is with firmware version 3.0. I am a new owner of the Firestore, so I do not know if this was available with prior versions.