The function is called every 100ms if possible. So 0.1 is correct.

The D term uses temperature change per second. As you see it computes a difference between 2 temperatures. One is inside an array of length 4 an dit points to the value 0.3s before. So multiplying with 3.333 gives change per second. Reason to use 0.3s distance is to get a more stable result then change between last measurement. Measurement errors get here a much to big impact.

Regarding overshoot, calibration is supposed to have that. See Extruder.cpp where values get computated:

Kp = 0.6Ku;

 Ki = 2*Kp/Tu;

 Kd = KpTu0.125;

 Com::printFLN(Com::tAPIDClassic);

 Com::printFLN(Com::tAPIDKp,Kp);

 Com::printFLN(Com::tAPIDKi,Ki);

 Com::printFLN(Com::tAPIDKd,Kd);

/

 Kp = 0.33*Ku;

 Ki = Kp/Tu;

Kd = KpTu/3;

 OUT_P_LN(" Some overshoot");

 OUT_P_F_LN(" Kp: ",Kp);

 OUT_P_F_LN(" Ki: ",Ki);

 OUT_P_F_LN(" Kd: ",Kd);

 Kp = 0.2*Ku;

Ki = 2Kp/Tu;

 Kd = Kp*Tu/3;

 OUT_P_LN(" No overshoot");

 OUT_P_F_LN(" Kp: ",Kp);

 OUT_P_F_LN(" Ki: ",Ki);

 OUT_P_F_LN(" Kd: ",Kd);

 */

You see the last set of equations would set it more conservative to have no overshoot.