How to specify initial states for simulink model in AC sweep analysis?

As I you have noticed I have another question related after many tries.

in the AC sweep block, there is an icon where it is written: System period length which means The period length of the unperturbed system in the demos of PlBuckSweep. I used the help but for me, I still don´t get what it means and how can this impact my bode plot?

-Start from model initial state uses the initial state values specified in the model - either in the individual blocks or in the simulation parameters.how can I use this method of obtaining the steady state analysis, I mean how do I specify the initial state? -I have noticed my system is not giving the result as the analysis does not stop for hours when trying to use the Start from unperturbed steady state method (I am simulating a DCDC boost converter with 4Mhz switch frequency with peak current control mode) thanks for your help