Translation:Shulchan Aruch/Orach Chaim/233
Chapter 233: Time of Minchah (Afternoon) Prayer, Containing Two Sections
One fulfills his responsibility for afternoon prayers when he does it after 6.5 hours [of daylight]. The primary period, per Rabbonon, is from 9 hours until night; and, per Rabbi Jehudah, [only] until Plag HaMinchah ("half of Minchah"), which is until one quarter hour before the end of eleven hours.
Gloss: We calculate these hour measurements according to the situation of each day, dividing the day into 12 [equal] "hours," even if the days are long. These are called "proportional hours."  Anywhere the sages measure time using [the term] "hours," they were measuring using these [proportional] hours.
The rule is that each person can choose the authority he wishes to follow, so long as one consistently follows one opinion. So, if one acts according to Rabbonon, and prays Minchah until night, he is never able [thereafter] to pray Ma'ariv (Evening Prayer) after Plag HaMinchah. So, too, if one acts according to Rabbi Jehudah, and prays Ma'ariv at Plag HaMinchah or later, he must thereafter be careful not to pray Minchah at that time.
Currently, since the custom is to pray Minchah until night, do not pray Ma'ariv before sundown. If one prayed Ma'ariv after Plag HaMinchah [but before sundown], he still satisfies the obligation, and if one is forced to, he may pray Ma'ariv starting at Plag HaMinchah.
Gloss: And for us [Ashekenazim], in the [Central European] states, that have the custom to pray Ma'ariv starting at Plag HaMinchah, one should not pray Minchah after [Plag HaMinchah]. If one did so, or was forced to, he satisifes his obligation, when he prays Minchah as late as night, which is until the Tzeth HaKochavim ("coming of the stars.")
One must wash his hands prior to praying, if he has water [available], even if they had not become dirty. He does not make a blessing [for washing].
(See above, Chapter 92, [One Who Has a Bodily Need, and Rules of Washing, and Other Preparations, for Prayer.] Gloss: Even one who was [in the midst of Torah] study when he got up [to pray], should wash his hands for prayer.
If one does not have water prepared, he need not wash.