Learn Hardcore Turkish: Okula geleli iki saat oldu. - It has been two hours since I came to school.

-(y)eli/-alı is a converb meaning “since (doing)”. It attaches to a verb stem to form an adverbial time clause. So geleli = “since (someone) came.” In the whole sentence, Okula geleli iki saat oldu, the structure is “Since [coming] to school, two hours have passed.”

Why is oldu (past tense of “to be/become”) used to mean “have been”?

Turkish commonly uses olmak in the simple past to express elapsed time up to now. İki saat oldu literally means “two hours happened/elapsed,” which corresponds to English “it’s been two hours.” With -(y)eli, this is the most natural way to say “It has been X time since…”

Is iki saat oldu interchangeable with iki saat geçti?

Often yes. Both can follow -(y)eli:

Okula geleli iki saat oldu.
Okula geleli iki saat geçti. Both mean “Two hours have passed since (coming to) school.” Geçti emphasizes the passage of time a bit more; oldu is very idiomatic with this pattern.

Why is it okula and not okulda or just okul?

Gelmek takes the dative (direction “to”), so you say okula gelmek (“to come to school”). Okulda is locative (“at school”) and wouldn’t be used after gelmek here.

Who is understood to have come? How do I specify the subject?

The subject of geleli is understood from context. You can make it explicit by adding a noun or pronoun:

Ben okula geleli iki saat oldu. (It’s been two hours since I came…)
Ahmet okula geleli iki saat oldu. (…since Ahmet came…)
Biz/Onlar okula geleli iki saat oldu.

How do I turn this into a yes/no question or a negative?

Question: Okula geleli iki saat oldu mu? (Has it been two hours since…?)
Negative: Henüz/Daha okula geleli iki saat olmadı. (It hasn’t been two hours yet since…)

How can I add nuances like “only/already/exactly” two hours?

“Only”: Okula geleli daha iki saat oldu.
“Already”: Context plus intonation, or add çoktan for longer spans: Okula geleli çoktan iki saat oldu (colloquial).
“Exactly”: Okula geleli tam iki saat oldu.

Can I say this with -den beri instead of -(y)eli?

Yes. A common alternative is a finite clause with -den beri:

Okula geldiğimden beri iki saat geçti/oldu. Meaning is the same. -(y)eli is shorter and very natural; -den beri is more general and works great with ongoing states as well.

What’s the difference between -(y)eli and forms like gelince or gelir gelmez?

-(y)eli = “since (doing)” with elapsed time: Okula geleli iki saat oldu.
Gelince = “when (he/she) came”: Okula gelince seni aradım.
Gelir gelmez = “as soon as (he/she) came”: Okula gelir gelmez seni aradım. They express different temporal relations.

How flexible is the word order?

Turkish word order is flexible. You can say:

Okula geleli iki saat oldu. (neutral)
İki saat oldu okula geleli. (focus on “two hours”)
Okula geleli oldu iki saat. (colloquial emphasis) Meaning stays the same; word order shifts focus.

How is geleli formed morphologically?

Root gel- + converb -eli → geleli. The suffix has two forms with two-way vowel harmony and a buffer consonant after vowels:

After a consonant: -alı/-eli (e.g., döneli, kalkalı)
After a vowel: -yalı/-yeli (e.g., başlayalı, arayalı) Choose a/e according to vowel harmony.

Can I use the negative with this pattern, like “I haven’t been to school for two weeks”?

Yes—negate the verb before -(y)eli to mean “since [the last time X happened] ⇒ X hasn’t happened for [time]”:

Okula gelmeyeli iki hafta oldu. (I haven’t come to school for two weeks.)
Seni görmeyeli çok oldu. (It’s been a long time since I saw you.)

Do I always need oldu/geçti at the end?

In full sentences, yes—something like oldu or geçti (or another main clause) is expected: Okula geleli iki saat oldu. Without it (e.g., Okula geleli iki saat), it sounds like an unfinished fragment.

Why not say oldum/olduk instead of oldu?

Here the subject is the time expression (“two hours”), not a person, so 3rd person singular is used: iki saat oldu. Saying oldum would literally be “I became two hours,” which is ungrammatical in this meaning.

Can I say geleli beri?

Yes, -(y)eli … beri can co-occur for emphasis or a slightly literary tone: Okula geleli beri ders çalışıyorum. But with the elapsed-time pattern, -(y)eli + oldu/geçti by itself is already complete and standard.