after starting the conversion, check for the GO/DONE in the ADCON 0(2nd bit) register to clear...ie..you are start the conversion by setting ADCON0, 2......and it will clear automatically after the conversion...
depend on the ADC clock source settings you can complete the ADC conversion in 16 or 200 uS. As faster is the ADC conversion than more noisy is the measured signal. In case you don't want 10 bits resolution you can make the conversion really fast