Fırında yemek varken zaman hızlı geçiyor.

Varken is the contracted form of var + iken.

• var = there is/are, exists, available
• iken = while/when (X) is So varken means “while there is (…)/when there is (…).” The negative counterpart is yokken = yok + iken (“while there isn’t/when there isn’t”).

-da/-de/-ta/-te is the locative case suffix meaning “in/at/on.” Which form you use depends on:

• Vowel harmony: last vowel back (a ı o u) → -da/-ta; front (e i ö ü) → -de/-te.
• Consonant voicing: after a voiceless consonant (p ç t k f s ş h), the suffix-initial consonant devoices to -t.

In fırın, the last vowel is back (ı), and the final consonant n is voiced, so we use -da: fırında = “in the oven.” Compare: şehirde (in the city), parkta (in the park).

Yes. fırındayken = fırında + iken, with a buffer y because fırında ends with a vowel.

• Fırında yemek varken… emphasizes the existence of food in the oven (“while there is food in the oven…”).
• Yemek fırındayken… emphasizes the state/location of the food (“while the food is in the oven…”). Both are natural; the nuance is very slight in this context.

Both are correct, but for “time,” Turkish often prefers çabuk:

• Zaman çabuk geçiyor sounds very idiomatic.
• Zaman hızlı geçiyor is also fine; it literally emphasizes speed. You can compare with daha: Zaman daha çabuk/hızlı geçiyor (“Time passes faster/more quickly”).

With var/yok for existence, the default is often a bare singular: yemek var = “there is food.”

• yemekler var = “there are (some) foods/dishes” (emphasizes plurality).
• bir yemek var = “there is a (single) dish/meal” (introduces one specific item). Your sentence uses the generic “there is food.”

Here it’s a noun meaning “food/dish/meal,” depending on context. Yemek can be:

• Noun: yemek (food/meal/dish) — as in this sentence.
• Verb (infinitive): yemek (to eat) — e.g., yemek istiyorum (“I want to eat”). Context disambiguates it.

You can, but it slightly changes the focus:

• Fırında yemek varken = “while there is food in the oven” (existence in that location).
• Fırındaki yemek varken = “while the food that is in the oven [exists/is available]…” (points to that specific, identifiable food using -ki “the one in/at”). Use -ki when you’re singling out that particular food.

Yes, you can move it:

• Fırında yemek varken zaman hızlı geçiyor.
• Zaman hızlı geçiyor, fırında yemek varken. A comma is optional but common when the subordinate clause comes second, especially in writing.

Use yokken:

• Fırında yemek yokken zaman yavaş/çabuk geçmiyor.
• Or more symmetrical: Fırında yemek varken zaman çabuk geçiyor; yokken yavaş geçiyor.

Primarily it’s temporal (“while/when there is”). In suggestions/imperatives it can feel like “since/while we have X available, let’s …”:

• Varken yiyelim = “Let’s eat while there is (some).” But grammatically it’s still a time clause, not a causal conjunction.

Yes:

• Fırında yemek olduğu zaman/olduğunda zaman hızlı geçiyor. These are correct and mean “when there is food in the oven.” Varken is shorter and very natural; olduğu zaman/olduğunda can sound a bit more formal or event-like (a specific time when it occurs).