It depends on how it is set up in your delay box. It is either an up or down not both.
You would need a manual for your box and then go through the progaming to see how it is set up. My brother used his the first time only to find out the time in the bump down was 0. Meaning no matter how many times he hit the button, the delay didn't change. He had to figure out how to program his.
Depending on the brand of box the manual is probably available online.
My brother's car also has a SLE, Starting Line Enhancer. Basically a air cylinder on the throttle. So he has a button for that also.