How long is a festival?

I just bought Drama and Poetry so now I can start a Festival

When I hover over the festival button is says

Hold a culture festival to make your kittens happy.(30% to the happines for a year).

I don't really understand it. Does this mean a festival is a full year, or is a festival until the end of a year?

When you click on the button hold festival a timer will start and will count down from 400 to 0.

When te timer hits 0 the bonus effect of 30% happiness will end and you have to spend another 1500 Manpower, 5000 culture and 2500 Parchment to get the 30% happines bonus.

So a festival will take for 400 days and not until the end of a year.

Festival don't stack so if you have enough resources to start another festival before the first festival is over you won't have a festival that is longer than 400 days

the code:

holdFestival: function(){
        this.game.calendar.festivalDays = 400;  //nope, they don't stack
        this.game.msg("The cultural festival has started");
        //TODO: some fun message like Molly Chalk is making a play 'blah blah'
    },

and

onNewDay: function(){

        if (this.festivalDays){
            this.festivalDays--;
        }

It is a whole year:

Below is the code that executes when you actually hold a festival (so press on the button). You see that there are 400 festival days. That is exactly the amount of days in a kitten-year. (from village.js)

holdFestival: function(){
    this.game.calendar.festivalDays = 400;  //nope, they don't stack
    this.game.msg("The cultural festival has started");
    //TODO: some fun message like Molly Chalk is making a play 'blah blah'
},

and each day such a festival day is subtracted, shown in the following code: (from calendar.js)

onNewDay: function(){

    if (this.festivalDays){
        this.festivalDays--;
    }