Protection of ADC inputs
Putting a 10K resistor on the input will not change things to any great extent.  Yes, technically it will slow down charging the sampling cap.  It will act as a low pass filter where the cutoff frequency is 1/(2*pi*R*C).  That works out to a cutoff frequency of 4.97 MHz.  So any frequency above 4.97 MHz will be significantly attenuated.

This ADC has several modes, but the quickest mode it has runs as 240 samples per second.  Meaning that it can handle frequencies less than 120 Hz.  The RC filter caused by the input cap and the 10K resistor has a frequency response that is still 4 orders of magnitude higher!  

In short, that 10k resistor on the input isn't going to do anything negative for you.