Ralph,

Below there is your second idea which counts up to 600 seconds and then turns on a led for 10 seconds and then turns off.

;PROGRAM TO DRIVE LED IN CURRENT SINK MODE
$TITLE (CURRENT SINK LED DRIVER PROGRAM, FLASH ON/OFF
$MOD51

ORG 0x0000 ; RESET START ADDRESS
JMP START ; JUMP OVER RESERVED ADDRESS SPACE
ORG 0040H ; PROGRAM START ADDRESS
START: CALL DELAY ;HOLDING DELAY
CLR P1.1 ;TURNS LED ON
call TenSec ;SETS FLASHING SPEED
SETB P1.1 ;TURNS LED OFF
JMP START ; REPEAT
DELAY: MOV R3,#60 ; TRIPLE LOOP HOLDING DELAY
TenSec: MOV R2,#0xxH ;The values xx & yy depend
LOOP1: MOV R1,#0yyH ;on your system clock
TAKE: DJNZ R1,TAKE
DJNZ R2,LOOP1
DJNZ R3,TenSec
RET
END

Cheers,
George