If you are not sure about ad times giving you correct values, you can make
an experiment:
Make some conversions changing tad every time and then display the results
of conversions.
I did that way when I wanted to insure correct values at different times. An
example of this in CCS C is:

unsigned int16 j;
char valor[]="    ";
unsigned int8 p1,p2,p3,p4;

   setup_adc_ports(sAN0|sAN1|sAN2|sAN3|sAN4|VSS_VDD);
   for(j=0;j<1000;j++) {
      setup_adc(ADC_CLOCK_INTERNAL);
      setAN(0);
      delay_us(4);
      p1 = leeAN;
      setup_adc(ADC_CLOCK_DIV_32);
      setAN(0);
      delay_us(4);
      p2 = leeAN;
      setup_adc(ADC_CLOCK_DIV_8);
      setAN(0);
      delay_us(4);
      p3 = leeAN;
      setup_adc(ADC_CLOCK_DIV_2);
      setAN(0);
      delay_us(4);
      p4 = leeAN;

      itoa(p1,10,valor);
      LCD_CursorYX(2,1);
      LCD_Print(valor);
      itoa(p2,10,valor);
      LCD_CursorYX(2,6);
      LCD_Print(valor);
      itoa(p3,10,valor);
      LCD_CursorYX(2,11);
      LCD_Print(valor);
      itoa(p4,10,valor);
      LCD_CursorYX(2,16);
      LCD_Print(valor);

      delay_ms(100);
   }

Take into account, it is not exactly the same you are talking about, as I
use C and fixed delays, but it is the most similar example of my code I
found.
It changes the AD clock and, thru a display, you can check wich values are
different, so wich is giving you incorrect values due to a faster clock.

2009/7/3 Nathan House <nathanpiclist@gmail.com>

> >Minimum means that time is enought to acomplish a conversion, so the more
> >Tad time you give, the more time you are wasting. So, minimum should be
> also
> >recommended in most cases, but that depends on how you do conversion and
> if
> >it's a speed critical aplication.
>
> So if I get an invalid value calculating the ADCS value using the minimum
> Tad time, should I just keep raising the Tad time until I get a valid
> answer?
>
> Equation 17-1 in the 30F family reference manual:
>
>  <http://roboticsguy.com/equation/rendered/images/70046E_equation_17-1.png
> >
>
> Solving for ADCS with my instruction time and the minimum Tad value:
>
> [image:
>
> http://roboticsguy.com/images/misc/70046E_equation_17-1_solving_for_ADCS.png
> ]
>
> Which equals: *-0.58335*
>
> If I make Tad 400ns then ADCS would equal 1. Is that what I should do?
>
> Thanks :)
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