Bitte kommen Sie in fünfzig Minuten zurück.

Because Sie with a capital S is the formal word for you in German.

• Sie = formal you
• sie = she or they

So the capital letter is important. In this sentence, the speaker is addressing someone politely or professionally.

Yes. This is a polite command/request, also called the formal imperative.

German uses different imperative forms depending on who you are talking to:

• Komm zurück! = to one person you know well
• Kommt zurück! = to several people you know well
• Kommen Sie zurück! = formal singular or formal plural

So kommen Sie is the correct form when speaking politely.

Because zurückkommen is a separable verb.

Its dictionary form is zurückkommen = to come back / return.
But in a normal main clause, the prefix zurück- separates and moves to the end:

• Sie kommen zurück.
• Bitte kommen Sie ... zurück.

When the verb is not split, it stays together:

• zurückkommen (infinitive)
• zurückgekommen (past participle)

It means fifty minutes from now.

So it gives a future point relative to the present: come back after fifty minutes have passed.

It does not mean the action lasts fifty minutes.
If you wanted to say for fifty minutes, you would usually use für instead:

• für fünfzig Minuten = for fifty minutes

Because fifty is more than one, so German uses the plural noun.

• die Minute = the minute
• die Minuten = the minutes

Compare:

• in einer Minute = in one minute
• in fünfzig Minuten = in fifty minutes

In this time expression, in is used with the dative.

You can see that more clearly in singular examples:

• in einer Minute
• in einer Stunde

With Minuten, the form does not look special because the plural already ends in -n, which is what dative plural normally needs anyway.

Because bitte here is just part of the sentence, meaning please. In normal German, you usually do not put a comma after it:

• Bitte kommen Sie in fünfzig Minuten zurück.
• Kommen Sie bitte in fünfzig Minuten zurück.

A comma would only appear if Bitte were being treated as a separate interjection for dramatic pause or special emphasis, which is not the neutral reading here.

Yes. Bitte is quite flexible.

Very natural versions include:

• Bitte kommen Sie in fünfzig Minuten zurück.
• Kommen Sie bitte in fünfzig Minuten zurück.

Both are correct. Starting with Bitte can sound a little more front-loaded and polite, while putting bitte after the verb is also extremely common.

You sometimes can, but the usual choice here is in fünfzig Minuten.

• in fünfzig Minuten = fifty minutes from now
• nach fünfzig Minuten = after fifty minutes have passed

In a direct instruction to return at a future time, in is the more natural and expected option.

They are often similar, but not always identical.

• zurückkommen emphasizes returning to a previous place
• wiederkommen can mean come back or simply come again

In this sentence, zurückkommen is especially clear because it focuses on returning after going away.