I think Henriks' idea of using a timer/counter is the way to go. This leaves you tons of time to handle other things while the counter works for you in the background.

There is no need to wait with any WHILE/WEND, PAUSE, etc.

Code:
CMCON = 0        ' Disable comparators
TRISA.4 = 1      ' RA4/T0CKI = input to TMR0 counter
PORTB = 0        ' clear all outputs on PORTB
TRISB = 0        ' PORTB outputs
ANSEL = 0        ' All digital 
 
' OPTION_REG setup for Timer0
' Prescaler to WDT with 1:1 prescaler for TMR0
' TMR0 clock is external input on RA4/T0CKI
' Increment on low-to-high transitions on RA4/T0CKI
' Internal pull-ups disabled
 
   OPTION_REG = %10101000 
   TMR0 = 0     ' Clear TMR0 count
 
Begin:
    IF TMR0 >= 20 THEN Ledas
 
    ' you have time to do lots of other thing here
    ' while Timr0 counts pulses in the background
 
    GOTO Begin
 
Ledas:
   TMR0 = 0    ' clear Timer0 count here
   HIGH Led
   GOTO begin
And if you prefer Timer0 to increment on high-to-low transitions on RA4, just change OPTION_REG = %10101000 to OPTION_REG = %10111000.