Although it is generally prohibited to make a large meal on Friday, in order not to infringe on the appetite one brings with him to his Shabbos meal, exception is made for a seudas mitzvah that should not be delayed. There are two instances of this: A pidyon haben and a bris milah (Rema, Orach Chaim 249:2). In these instances, the Bach rules that the seudah should be made before the “tenth” hour, which is usually understood to mean in the afternoon, halfway between midday and sunset.
The Levush contends that if you cannot have both seudos, Shabbos and bris, the bris seudah should be done even at the expense of the Shabbos seudah, because both are seudos mitzvah, and you should perform whichever one comes first, without concern that as a result the second will not take place (Orach Chaim249:2). The Bach appears to disagree with this Levush.
