There is a pink one and a white one. The pink (5mg) should last about 4 hours while the white (10mg) should last about 8. Nanook, as you said though, each affects people differently. They are not designed to knock you out, they are designed to allow your normal sleep pattern to commence. A small amount of alcohol just makes this more intense.

As an aside, though, I love one of the side effect warnings that accompany it. The product may cause drowsiness if taken.