The conversion time differs depending on the model number of the PIC microcomputer, but the conversion time is the sum of the acquisition time and the conversion time.

The PIC16LF1554 series is explained below as an example.

Driving the ADC requires time to charge the internal sample-and-hold capacitance.
That time is called the acquisition time, and 5 us (see Acquisition Time) is required as standard.

After that, sequential conversion is performed, but in the case of 10-bit ADC, it takes 11 times the conversion clock ADC Internal FRC Oscillator Period (see 11 TAD, Conversion Time).

ADC Internal FRC Oscillator Period is generated by dividing the system clock and can be set between 1us and 6us.

Below is an example of the conversion time when operating at maximum speed.
ADC Conversion Time = Acquisition Time + Conversion Time * ADC Internal FRC Oscillator Period
= 5.0us + 11TAD * 1.0us
= 16.0us

From the above results, since the minimum period is 16us, it cannot operate at a speed of 62.5Ksps or more per second.