The earliest time for Shabbat candles

Hi,

We have been learning about lighting Shabbat candles.

We have said that one must light before sunset, adding from mundane time to the sacred time of Shabbat. Nonetheless, one may not light too early, before the time we call "Plag haMinchah," "The midpoint of Minchah." This is because Plag haMinchah is the earliest time recognized within Jewish law as nightfall.

One may calculate this Plag haMinchah time by the following methods-

A. For followers of the Vilna Gaon's practices:
1) Take the number of minutes between sunrise and sunset, and divide it into twelve units.
2) Multiply one of those units by 1.25.
3) Subtract that period of time from sunset, and you will have found Plag haMinchah.

B. For followers of the Magen Avraham's practices:
1) Take the number of minutes between first light and when the stars emerge, and divide it into twelve units.
2) Multiply one of those units by 1.25.
3) Subtract that period of time from when the stars emerge, and you will have found Plag haMinchah.

For example: If the stars emerge at 4:48 AM and sunrise is 6 AM, and sunset is 6 PM and the stars emerge at 7:12 PM, then the Vilna Gaon will mark Plag haMinchah at 4:45 PM, and the Magen Avraham will mark Plag haMinchah at 5:42 PM.

(Code of Jewish Law Orach Chaim 263:4)

Have a great day,
Mordechai