I'd like to know the name and a few details of a certain time-keeping structure in the human brain
You are probably referring to the suprachiasmatic nucleus.

Note that, although this is the central clock, there are also so-called "peripheral clocks", for instance in the liver, pituitary and other organs that can finely tune rhythms in the organism.

You may also want to have a look at the Wikipedia page for circadian clock and references therein.