Now that we have switched to DST many people are going to start making early shabbos so I would like to discuss some of the relevant halachos relating to early Shabbos.
The gemara in Berachos at the beginning of the fourth perek has a dispute between R' Yehuda and the Chachamim whne the time to daven mincha ends. R' Yehuda holds until plag hamincha (10.75) and the Chachamim hold until night (which from now on we will call sunset like the opinion of the Gra). The gemara explains that everyone agrees that the tefilos are related to the korbanos and the dispute is when is the last time that the תמיד של בין הערבים can be offered, the chachamim hold until sunset amd R' Yehuda holds until plag hamincha. Given this, I would not have assumed that there is a machlokes relating to maariv, I would have thought that everyone agrees that maariv is at night. However, we see from the gemara explicitly that this is not so. The gemara states that there is a machlokes as to when the zman of maariv starts as well, the zman of maariv starts when the zman of mincha ends (why this is so is not so clear).
The gemara paskens that דעביד כמר עביד ודעביד כמר עביד, in other words you can do like either one. The rishonim point out that you have to be consistent at least in a single day.
Based on R' Yehuda the gemara states that a person can be מקבל שבת from plag hamincha.
II. When should you daven?
In America you have the ubiqitous 7PM early shabbos minyan. This is problematic for 2 reasons.
1. The latest Plag Hamincha gets in NY is 6:56, this means that if you daven at 7PM you are davening both mincha and maariv in the time between plag and sunset all the time. This is called תרתי דסתרי, meaning a contradiction. By davening mincha after plag you are going like the Chachamim and saying that this time is day, by davening maariv before sunset you are going like R' Yehuda that this time is night, on the same day this is clearly a contradiction. The Mishna Berura paskens that on erev shabbos if this is the only way that you can get a minyan that it is ok, however it is certainly not לכתחילה a good idea.
2. There is a din that you are not allowed to start a meal 1/2 hour before the time of krias shema which is צאת הכוכבים .צאת הכוכבים is approximately a 1/2 hour after sunset, so you cannot start a meal after sunset. During the week most people forget about this halacha and rely upon the fact that they daven maariv with a set minyan every night (e.g. 8 or 9PM), however Friday night this doesn't apply as you already davened maariv early. Let's look at a concrete example.
Sunset is 7:55. Davening takes 40 minutes, you stand around and shmooze for 5 minutes after davening and it takes 5-10 minutes to walk home. By the time you get home it is 7:55 and you aren't allowed to make kiddush and start the meal because it is within a half of hour of the zman of krias shma.
Based on the above, the best thing to do is to daven mincha right before plag and kabalas shabbos maariv right after. Because plag is 1.25 hours (zmaniyos) before sunset you don't have a problem with 2 either.
If everyone wants to have a set time, in NY I would recommend 6:40 instead of 7. For about 2 months in the summer plag is between 6:45 and 6:56 and therefore "by accident" you end up davening mincha before plag.
III When the should the wife light candles?
Candles cannot be lit before plag, if they are they need to be relit. The question that comes up is does the kabbalas shabbos of the husband affect the wife? Can she do melacha after he is mekabel shabbos? R' Moshe has a teshuva about this where he says that she is not affected and she can do melacha, many others agree as well. However, some poskim disagree. Therefore, the best thing to do is to have the wife light within the first 15 minutes after plag to be machmir for this opinion. If the wife cannot finish all the work in that time she clearly has who to rely on to do melacha even after.
to be continued ...