The warmup time is applicable to an CCFL backlit LCD monitor too. The cold cathode fluorescent lamp requires time to reach full brightness, but in a much shorter time than required for an CRT display.
The warmup has nothing to do with causing damage. The warmup period is required to give a truer rendition of colors. If you didn't allow for warmup, and you ran the display optimization wizard when you just turned on your display, you will end up with the wrong color balance as the display warms up.