load the sketch blink without delay.
that gem has the key to timing for you and multiple timers can run concurrency.
one thing about temperature control. the simplest is to have the fan on low speed if the temperature is between X plus 10 and say, X plus 20, and then on high speed if it is X plus 21.
on the way down, as it cools, keep the fan running until X plus 15, or X plus 5 that way, it will not turn on and off and on and off.