Big events require some preparation, perhaps at least on the eve of that event. In the Church, feasts like that of Sts. Peter and Paul is celebrated from the eve.
Bigger events may require a lengthier preparation perhaps even a week. In the Church, she usually takes 8 days (an octave) or even 9 days (a novena) to prepare for them. For example, tomorrow we begin the novena to prepare for the feast of the Immaculate Conception of Mary on Dec 8th (more on this later).
Humongous feasts in the Church take a month to prepare for. The Church has 2 of these feasts. The first is the sacred Easter Triduum ("triduum" meaning 3 days) when we celebrate the suffering, death and glorious resurrection of our Lord. To prepare for this, the Church takes 40 days called the "Lenten" period.
The second is what we begun today: almost 4 weeks of "Advent" to prepare for the humongous feast of Christmas.
Here's a 2min video to explain more about Advent.
29thNovember 2015