"Saat birde öğle yemeği yiyorum." Translation: I am eating lunch at one o'clock.
Why it is "birde" not "Bire"?
Bir + "e." Bire - "to one." This suffix gives a different meaning.
The (locative) case suffix. Location "in", "at" or on a "place." In this example "in time."
Turkish (nominative) - Otel. Turkish (locative) - Otelde. - At the hotel.
Bir + "de." Birde - "at" one o'clock. The correct suffix makes the word pronunciation & consonant, vowel harmony right when spoken.
Time is abstract. When it becomes specific, "Saat birde" at one o'clock makes the chosen time an abstract location without being a physical place. The locative suffix is therefore correct.
My personal grammar notes not Duo's
The dative case.
We add the dative case suffix (y) -e to the indirect object. In English it equates to prepositions "at", "to" & "for."
Tips & notes
The Dative case in Turkish is used to describe movement towards something and for indirect objects. An indirect object tells “to whom or for whom” an action is being done. It always tells the recipient of the direct object.
I gave her a hug.
I told him about the event.
We showed them the cake.
Forming the Dative case is very simple, considering the amount of knowledge you have under your belt now. The suffix is “-(y) A.” The suffix obeys 2-way vowel harmony and uses a buffer -y- when attached to a word that ends in a vowel. Consonant harmony will often happen at the end of words that end with /p t k ç/. Simple, right? It is a great way to review concepts while still learning something new. Here are some examples:
English - Park
Turkish Dative - parka.
To the park.
şapka. şapkaya - to the hat
domates. domatese - to the tomato
fare. fareye - to the mouse
fareler. farelere - to the mice
köpek. köpeğe - to the dog
shahidmecc, you ask an interesting question! I read back the sentences of Duolingo time's skill: we only have three sentences using "saat": "saat iki buçuk"='it is half past two". "Saat birde öğle yemeği yiyorum"="i am eating lunch at one". "Saat sekize beş var"= it is five to seven". Have a look there: https://duolingo.fandom.com/wiki/Turkish_Skill:What%27s_the_Time%3F, about "what time is it ?" and "at what time?". Rather interesting. My conclusion is that "saat" is optional!