A reader has lately commented on the original entry and has provided the following additional historical information. Since it is that time of year again, I thought it was fitting to post the comment in its entirety.
This old custom originates from the Territory of the former Austrian-Hungarian Monarchy. The Alternative names of the Rorate Mass in Hungary are the daybreak Mass, Angel Mass, Golden Mass or Mass of Blessed Virgin. The Rorate Masses were said in Hungary since the 12th Century. According to the Ordo Stigonienis these early morning Masses were said in white. If it was a Solemn Mass, the Gloria and Credo were also sung. This special privilege was kept after the introducing the Tridentine Rite, as a Hungarian custom. After Vatican II these Mass are said in purple. In Hungary traditionally these Masses were started in the dark at 6:00 am and finished after sunrise. This custom is continued in lot of Hungarian Churches, which are usually full on these mornings. Young people likes to go there and they are competing who can go to more Rorate Mass. This is a very nice practice of virtue.