What are you saying? The Zener is fast enough to catch a millisecond peak. Also, an analog pin won't be damaged with ANY voltage above Vcc - as long as there is current limiting to less than 10mA and you have a few hundred pf of capacitance on that pin to GND.
The cap is needed in case a picosecond pulse (spark discharge) has a chance to raise the voltage at the input pin faster than the body diode (the input pin to Vcc diode inherent in the PICs design) can start conducting.
But you already said you have an R/C network. That will be enough.