This is a regular Advent Calendar built in JS, with 24 doors for the days of Advent (Dec 1 - Dec 24). A door can only be opened on or after the specific date on it. This means that the Calendar is inactive before December.
In order to test the Calendar before December, please comment out the month checker in the /scripts/calendar.js
file, in line 24 in the following way:
if( /* ( currentDate.getMonth() + 1 ) < 12 || */ currentDate.getDate() < day ) {
This way the Calendar will only check the day of the current month, but not the current month of the year, so it can be tested before December.
You can find demo on http://hongkiat.github.io/advent-calendar/