> The interrupt won't get lost, just delayed 66mS according to your figures.

Here's how I time it in CCS C, if anyone is interested.  Its not perfect,
but its within a few ms, which is close enough for the questions I have.

#define CLOCK_SPEED 4000000
#define MS_PER_SECOND       1000
#define TICKS_PER_OVERFLOW  65535
#define CLOCK_PER_FOSC      4
#use delay(clock=CLOCK_SPEED)
....
int16 ticks, overflows;
int32 execution_time;
int32 milliseconds = 0;

#INT_TIMER3
void
int_timer3_isr (void)
{
  overflows += 1;
}

void
setup_execution_timing()
{
  setup_timer_3 (T3_INTERNAL);
  set_timer3 (0);
  enable_interrupts (INT_TIMER3);
  enable_interrupts (GLOBAL);
}

void
start_execution_timing()
{
  disable_interrupts(INT_TIMER3);
  overflows = 0;
  ticks = 0;
  milliseconds = 0;
  set_timer3 (0);
  enable_interrupts (INT_TIMER3);
}

int32
stop_execution_timing()
{

  disable_interrupts(INT_TIMER3);
  ticks = get_timer3();
  milliseconds = (overflows *
    (TICKS_PER_OVERFLOW / (CLOCK_SPEED / CLOCK_PER_FOSC / MS_PER_SECOND)));
  milliseconds += ticks / ((CLOCK_SPEED / CLOCK_PER_FOSC) / MS_PER_SECOND);
  return milliseconds;
}

main()
{
  setup_execution_timing();
  start_execution_timing();
  code to be timed ......
  .......
  execution_time = stop_execution_timing();
}
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