We are beginning siman 11, where the Chayei Adam discusses the preferable time to daven mincha. Arguably, there is no advantage to davening mincha earlier. As we learned (S0030), the generally preferable time to daven mincha is after mincha ketana.
As some background, we will discuss the reason the preferable time to daven is after mincha ketana. Mincha corresponds to the afternoon korban tamid. That korban could be brought as early as 6.5 hours after sunrise; however, it was only brought that early when erev Pesach was erev Shabbos. The korban pesach has to be brought as a korban and then be brought home to be roasted before Shabbos. The korban pesach is the only korban brought after the korban tamid. Since it is brought after the korban tamid, the korban tamid was brought as early as possible in order to facilitate bringing the korban pesach. Otherwise, it was generally brought much later. Therefore, it is generally preferable to daven mincha later as well.
The issue, however, is that Chazal instituted prohibition against doing certain actions after the time of mincha has arrived, out of concern that those actions may cause a person not to daven mincha. The concern is both in terms of actions which may prevent a person from davening, and actions which may cause a person to forget to daven. For example, Chazal prohibited eating a large meal before davening mincha. If the meal began before the zman, one may continue (until the end of the zman; they must certainly daven at some point before the zman is over).
One of the prohibitions instituted is not to go to the merchatz (bathhouse) before davening mincha. Since the merchatz is warm and steamy, they were concerned a person would get tired or faint and end up missing mincha. Therefore, Chazal prohibited entering a bathhouse once the zman mincha takes place. The zman in question is a machlokes in the Gemara, with one opinion that it is already assur to enter the merchatz from mincha gedolah, and one opinion that it is only assur from mincha ketana.
Based on this point, the Chayei Adam writes that even though he agrees that in general, the preferable time to daven mincha is after the zman of mincha ketana, on erev Shabbos it is preferable to daven mincha gedola. It is certainly preferable if one plans to go to the bathhouse, as it is arguably assur to go to the bathhouse once the zman mincha gedolah has occurred.
Practically, we do not have the concern of a merchatz nowadays. A shower does not approximate the concern of a bathhouse, and, although some poskim suggest a mikvah may be the equivalent of a merchatz, a mikvah which does not have a steam room does not have this concern. A mikvah with a steam room for use after the mikvah would be the equivalent of a merchatz, and this halacha would apply in such a case.
Another halachic concern is getting a haircut on erev Shabbos. Chazal were concerned that something may happen in the middle of the haircut, such as the machine breaking, which would prevent the person from davening mincha. The above argument as to which Mincha time we are referring to applies here as well. Again, it would be appropriate to daven mincha gedolah, if needed, before getting a haircut to avoid this issue.
The Chayei Adam adds that even if one does not have a bona fide halachic concern, there is another concern, which we will discuss tomorrow, be’ezras Hashem.
Although it is generally preferable to daven mincha ketana, on erev Shabbos it is preferable to daven mincha gedolah.