Translation:I go home at 6 P.M.
おかえり is itself a shortening of おかえりなさい. なさる is the sonkeigo form (used to show respect to others) of する ("to do"), and なさい is its imperative form. (The prefix お is also an honorific prefix.)
More info here: https://en.wikipedia.org/wiki/Honorific_speech_in_Japanese
かえり is from the verb かえる which means to return/go back. いえ is not necessarily implied - you could be returning anywhere. Also lots of languages seemingly "repeat" themselves unnecessarily - it's just how those languages work. Greek is particularly well known for this - or at least classical Greek is. Some examples - sacrifice the sacrifice, plant the plant, draw the drawing.
It doesn't have a very narrow definition. 6 o'clock pm is just simply incorrect. There is no need to include 'o'clock' - the 'pm' already lets us know that this is a reference to time. Also you would never say o'clock pm or o'clock am for that matter. You would say am or pm or o'clock but not o'clock and am/pm together.
'Go home' is the departure from a location, while 'get home' is the arrival at a location. 'I will go home at 6 pm and get home at 6:30 pm.'.
In Japanese, 「午後6時に家に帰って、6時30分に家に到着します/着きます。」(I go home at 6:00 pm, I arrive home at 6:30 pm.).
Up until the point that you actually enter the residence, you are 帰り中 (returning).
There is some overlap (I hesitate to say misuse) between how 帰る is used, with some using it to indicate arriving home. The principal meaning, however, is to depart a location.
It definitely sounds redundant in English. You should consider, however, that in Japanese 家(いえ)に帰(かえ)る is the proper way to say 'return to one's own home', with 帰る just being a shortened version of said expression, with the 私の家 being implied.
帰る doesn't always mean one's own personal residence.
For example, you can say 実家(じっか)に帰る (return to one's family home/childhood home) or 故郷(ふるさと)に帰る (return to one's hometown).
家に帰る - Return home.
(家に) 帰る - Return (home).