org 100h

mov al, 2ch ;get system time
mov bl, dh  ;dh = seconds
int 21h
mov ah, 2   ;print _
mov dl, bl   ;output
int 21h
mov ax,4C00h
int 21h       

org 100h

;DOS 1+ - GET SYSTEM TIME
;
;AH = 2Ch
;
;Return:
;CH = hour CL = minute DH = second DL = 1/100 seconds
mov ah, 2ch ; You was setting AL instead of AH here, so you was calling an unspecified function here
int 21h

;DOS 1+ - WRITE CHARACTER TO STANDARD OUTPUT

;AH = 02h
;DL = character to write
; BUT, we have to convert the number to ASCII first
mov al, dl
mov ah, 0
mov cl, 10
div cl

mov dh, ah
mov dl, al
add dl, '0'
mov ah, 2
int 21h

mov dl, dh
add dl, '0'
mov ah, 2
int $21

;KEYBOARD - GET KEYSTROKE
;
;AH = 00h
;
;Return:
;AH = BIOS scan code AL = ASCII character
xor ax, ax
int $16  ; Just halting execution until some key is pressed.

mov ax,4C00h
int 21h    

; You was setting AL instead of AH here, so you was calling an unspecified function here

erm the idea is to get the seconds from 0..99