Yes, you are correct.
At the moment, iOS does not provide a direct method of controlling the backlight so I can't shut it off. However, there is an indirect method of shutting off the backlight using the phone's proximity sensor functionality. The method is a bit of hack as you will need to have some method of reliably covering the proximity sensor to keep the display off. However, I think it is a good addition.
An upcoming TimeLapse update will do just this.