Learn Hardcore Turkish: Siz ne acele edin ne de gecikin; tam saatinde geliniz. - Neither rush nor be late; please arrive right on time.

“Siz” explicitly addresses the listener(s) politely or plural (“you” formal/plural). It adds emphasis and clarity but is not required; the imperative already implies “you.” All of these are fine, with slightly different tone:

Siz ne acele edin ne de gecikin; tam saatinde geliniz. (emphatic, formal)
Ne acele edin ne de gecikin; tam saatinde geliniz. (formal, a bit less emphatic)
Sen ne acele et ne de gecik; tam saatinde gel. (informal singular)

Why do “edin” and “gecikin” look like positive imperatives even though the meaning is “don’t hurry and don’t be late”?

In Turkish, the pattern “ne X (yap) ne de Y (yap)” means “neither do X nor do Y,” and it commonly uses the bare/positive imperative forms. So:

Ne acele edin ne de gecikin = Neither hurry nor be late. Even though “edin/gecikin” are positive imperative forms, the “ne … ne de …” construction makes the overall meaning negative (“don’t do either”).

Could I say it with explicit negative imperatives instead?

Yes. A very natural alternative without “ne … ne de …” is:

Acele etmeyin, gecikmeyin; tam saatinde gelin(iz). If you want to keep the “ne … ne de …” structure, keep it parallel:
Ne acele edin ne de gecikin… (as given), or
Ne acele etmeyin ne de gecikmeyin… (both negative, also possible but less common in speech). Avoid mixing one positive with one negative inside the same “ne … ne de …” pair.

Why “geliniz” instead of “gelin”? Is there a tone or register difference?

Both address “you (plural/formal).”

gelin: neutral-polite, common in everyday speech.
geliniz: more formal/ceremonial, seen in signage, announcements, or very polite speech. Your sentence mixes “edin/gecikin” (-in) with “geliniz” (-iniz), which is acceptable but slightly inconsistent in register. To keep one tone:
Everyday: “Siz ne acele edin ne de gecikin; tam saatinde gelin.”
Very formal: “Siz ne acele ediniz ne de gecikiniz; tam saatinde geliniz.” (This is grammatically fine but sounds quite stiff.)

What exactly does “tam saatinde” mean?

It means “exactly at the appointed time,” i.e., neither early nor late. “Tam” intensifies the idea of precision. Without “tam,” “saatinde” already means “on time,” but “tam saatinde” stresses exactness.

Why is it “saatinde” and not “saatte”? What’s going on morphologically?

“saatinde” is:

saat-i-n-de = saat (hour) + 3rd person possessive -(i) + buffer -n- + locative -de Literally “at its hour,” which is an idiomatic way to say “at the right/proper time.” By contrast, “saatte” is simply “at the hour,” a literal location-in-time, not the idiom “on time.”

Could I use “zamanında” or “vaktinde” instead of “saatinde”? Any nuance?

Yes:

tam zamanında = exactly on time (broadly “in a timely manner,” not tied to a clock hour)
tam vaktinde = exactly at the right time (very close to “saatinde,” slightly more general than a specific hour) “tam saatinde” implies the scheduled hour/minute more strongly; “zamanında/vaktinde” can feel slightly broader.

Why “acele etmek” and not something like “acele yapmak”?

“Acele etmek” is the fixed verb phrase meaning “to hurry,” using the light verb “etmek.” Many nouns form verbs this way (e.g., “yardım etmek,” “sohbet etmek”). “Acele yapmak” is not idiomatic.

What’s the difference between “gecikmek” and “geç kalmak”?

Both mean “to be late,” but:

geç kalmak: very common in everyday speech for people (Ben geç kaldım = I’m late).
gecikmek: slightly more formal or used for processes/events (Uçak gecikti = The plane was delayed). For a person, “geciktim” exists but sounds more formal/less common than “geç kaldım.”

Does “ne … ne de …” always need the “de”? Can it be “ne … ne …” only?

You will hear both. “Ne … ne de …” is the more typical written form and reads smoothly. Omitting “de” is possible in some contexts (Ne o ne bu), but with verbs many speakers prefer including “de.” In this conjunction, it’s written as “de” (not “da”).

Why is there a semicolon?

It separates two closely related instructions: the balanced prohibition (“ne … ne de …”) and the positive directive (“tam saatinde geliniz”). A comma would also be acceptable; the semicolon gives a slightly clearer pause.

How would I say this to one friend informally?

“Sen ne acele et ne de gecik; tam saatinde gel.”

How can I soften the tone politely?

Add “lütfen,” or rephrase as a request:

Lütfen ne acele edin ne de gecikin; tam saatinde gelin.
Lütfen tam saatinde gelir misiniz? Ne acele edin ne de gecikin.
Rica ederiz, tam saatinde geliniz.

Can you break down the imperative endings I’m seeing?

et-in = do (you pl./formal) → “edin”
gecik-in = be late (you pl./formal) → “gecikin”
gel-iniz = come (you pl./formal, more formal) → “geliniz” The -in/-ın/-un/-ün variant follows vowel harmony (et → edin; bak → bakın; oku → okuyun; düşün → düşünün). The longer -iniz/-ınız/-unuz/-ünüz is a more formal variant.