The earliest time for candle-lighting

Hi,

One may not accept Shabbat at just any time on Friday - it must be relatively close to evening, since Shabbat is supposed to be the 7th day of the week. The earliest time one may accept Shabbat is a time called "Plag haMinchah."

We calculate Plag haMinchah this way:
1. Take the time between sunrise and sunset and divide it by 12. Each 1/12 unit is called an "hour."
2. Subtract 1.25 of these hours from sunset. The resulting time is Plag haMinchah.

For example: One day there were 9 hours and 37 minutes between sunrise and sunset, so each "hour" was 48.08 minutes. 1.25 "hours" were then 60.1 minutes. Sunset was 5 PM, so Plag haMinchah was 4 PM.

(Code of Jewish Law Orach Chaim 263:4)

Have a great day,
Mordechai