Timing advacment, how much?

[P2Motorsport240sx]

I 've heard adjusting you timing a few degrees can get you a couple hp, not alot but something. How much to advance it. or retard it? I've notice on the crank pulley it has degree markings. When i have the timing light out and adjust the timing do i want the timing to move out clockwise toward the 20 degree Before Top Dead Center mark our counter clockwise toward the 5 degree After Top Dead Center mark.

crank pulley markingsATDC..................................................................................BTDC5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

what is stock timing set at?I have MSD ignition set up if that makes a difference