I see, depend you how/where set your shutter speed,
if you set the shutter speed in your camera, the interval time is start from the signal send to your camera to open shutter to the next signal, so you need to be careful about the total time of your shutter speed and camera writing speed not longer than the interval time.
if you are using a intervalometer to set shutter speed, the interval time starts from last shutter close to next shutter open.
one last question... ermm i know for time lapse, there is no need to shoot in raw...
so shooting in jpg... do u shoot in large, medium or small?
i read online that small is sufficient enough for a HD video... true?