Stardates Explained - 20171207.1900

You don't understand the stardates?
Take, for example, 20171207.1900.

Let me stick some spaces in some helpful places:
2017 12 07 . 19 00

That better?

20171207 means 7th Dec 2017, and
1900 is in 24-hour clock format, IE 7:00PM

Stardates in the Star Trek universe work in an entirely different way. Wikipedia has a good explanation on how they work.

Events on this stardate