From the great stoner movie "Shawn of the Dead."
2 seconds is the theoretical time it takes to do something totally unnesecary or dumb.

The code you use so as not to get caught when you see a really hot girl and need to alert your buddy.

When somebody is doing something undesirable or acting like an idiot they have 2 seconds to stop what they are doing. Commonly used along with "Yoo K".