The first allusion to Advent's being reduced to four weeks is to be found in the ninth century, in a letter of Pope St. Nicholas I to the Bulgarians. The testimony of Ratherius of Verona ...

1 each for the four weeks of Advent. The holder can be placed in a shallow platter containing some water. Place the candles in the holder securely, then drape the boughs of fir around the holder ...

Advent is four weeks long and marks the beginning of the Christian year. The first Sunday of Advent is always four Sundays before Christmas, which means it could be as early as 27 November.