Fuzzy Logic Controller - 120v Silicone heat pad to Metal shelf - Question on output for temp delay

I want to implement a FLC to control a tray heater driven with 120vac. I have a Zero cross detector that fires 120 times per sec. I plan on having the heater control be PWM based. Current thoughts are a period of 3 sec which is 360 ZC tics -- with control being how many of the tics are on. I have not yet mapped my PWM control to temperature yet (waiting on hardware) but plan on mapping final tray temp verses PWM over the temp range I need to control. I'm aware that there will be a lag between setting the PWM value and reaching a stabilized output temp (this is part of my FLC controller question). Input to the FLC is delta temp error, possibly rate of change of temp error if that should be in the FLC or be used to modify the FLC output (question). I believe the FLC (as with PID) assume a detectable error as soon as an input is made. A lag in the mix is what I'm not sure of handling. I could have the FLC produce a crisp PWM value based on zero lag and then have a function to modify that PWM value to compensate for lag (if this is good direction - not quite sure how to do that). Can/should Temp error rate of change be a FLC input to compensate for lag? If so, please explain how. I'll have hardware in a month to test with - right now just trying to understand the best way to control the PWM output value.