The average sampling time is 50uS although this will depend on the capacitance of the external circuitry you are sampling. I refer you to the ADC chapter in your PIC's Datasheet.

Also please do a search on this forum - there are plenty of examples already posted (including a complete program to read six ADC's and Datalogging the results, that I posted less than two weeks ago). Reading about the ADCIN command in your PBP manual is also a good place to start...