I've bought a Nikon D800 a month ago. I'm trying to turn on the opportunity for Time lapse photography, but my camera doesn't give me the chance. Is it something to do to unlock this choice?
I would recommend taking a look at the Nikon D800 manual which can be found online here.
Page 207 of the manual describes the features of the D800 and time lapse photography. You also will want to pay particular notice to the tips of the bottom of page 209 where it describes what modes time-lapse does not work in.
If you have a question beyond something that the manual already describes then I would come back here and ask it in a new question.
All you have to do is set the time/date in the setup menu and it will work.