I would take a different approach, which did not rely on delay() for timing. I would calculate seconds from midnight from the h, m & s from the rtc. Then I would come up with a formula/function which calculates the brightness/heat at a given time (in seconds) for a led in a given position. Then, once per second, or every 5 seconds, I would read the rtc and use the function to recalculate each led's brightness, then update the strips.