פירוש על ברכות 53:15

And he did not interrupt the prayer of - That is to say, he did not make a break between Rabbi Yirmiyah and the wall in order to pass before him and sit in his place, rather he stood at his post.

THAT RAV PRAYED THE SHABBAT [PRAYERS ON] THE EVE OF SHABBAT. The Gemara shows that one may act in accordance with R’ Yehudoh’s opinion and say maariv immediately after the half minchoh. This can be seen fro Rav, who said the Shabos maariv prayers on Friday afternoon after the half minchoh period. This is acceptable only according to R’ Yehudoh. The Rabanan do not allow for saying maariv early. Tosfos raises another problem with saying maariv early on Friday afternoon. This is bewildering. For the Gemara says in perek Bameh Madlikin (Shabos 23b) when discussing the proper time to light the Shabos candles, provided that one should not light too early before nightfall or too late. When one says the maariv prayers at the half minchoh, he is going to light the candles before he begins to pray, it seems that this would be too early, and the Gemara clearly states that one should not light the candles too early.
And we can answer; that there in Shabos 23b where the Gemara says that one should not light too early, it is speaking of when one is not accepting the Shabos upon himself, he is lighting the candles but expects to continue working. It is only then that we are told not to light the candles too early, but here in our Gemara, we are speaking of when he accepts Shabos and stops working immediately. Therefore, it is not considered too early to light the candles even though it is well before nightfall.
And the reason that it is acceptable to say maariv immediately after the half minchoh is because he, Rav, holds like R’ Yehudoh. And so too, the others mentioned later that said the Post-Shabos prayers on Shabos after the half minchoh, that is because they hold like R’ Yehudoh as far as the evening prayers are concerned, that it can be said an hour and a quarter before nightfall.
There is much disagreement about the correct text of the next portion of the Tosfos. We will follow the text that appears in the Tosfos HoRosh on this subject. This is by no means a declaration that this is the correct text; it is merely the simplest one to follow in the context of how Tosfos is presented. Even though, we say that one who usually says maariv after the half minchoh cannot say minchoh at that time, this is only a ruling that applies to prayer not to other areas of halochoh and it is not prohibited for one to do work erev Shabos immediately after the half minchoh when he did not accept Shabos by saying maariv.
And so too, as far as the issue of adding to Shabos and Yom Tov and Yom Kipur, that it is established for us that the obligation to add some time from the previous day to the Holy day by discontinuing our work prior to the exact beginning of the Holy Day is a Torah obligation, even so it is not required to have such a great amount of time as from the half minchoh till nightfall. It is certainly sufficient to add a relatively small period to the Shabos or other Holy Day to fulfill the Torah obligation to add some time. It is certainly not necessary to begin the holiday at the half minchoh time, even according to R’ Yehudoh.

And he did not interrupt the prayer of Rabbi Yirmiyah, as he did not step in front of him - And we learn from this that it is forbidden to pass in front of people praying, and specifically in front of their faces, but regarding their sides we aren't worried about just passing by.

By passing in front of him to resume his seat.

Although it is not yet dusk.