Learn Hardcore Turkish: Otobüs belli saatlerde geçiyor.

Turkish doesn’t use articles. Nouns remain unmarked in the nominative case, and context tells you whether it’s “a bus” or “the bus.” So otobüs simply stands for “bus” without any extra word.

Why is the verb in the present continuous form geçiyor when we’re talking about a regular schedule?

In Turkish, habitual or scheduled actions commonly take the present continuous suffix -iyor. Although English uses the simple present (“the bus passes”), Turkish expresses ongoing or repeated events with -iyor, so geçiyor covers both meanings.

What does belli mean in this sentence?

Here belli means “certain” or “specific.” It describes saatlerde, telling us that the bus passes at particular, pre-determined times, not just at random hours.

Why is it saatlerde instead of saatler or saatte, and what do the suffixes -ler and -de mean?

saat = “hour.”
-ler makes it plural (saatler = “hours” or “times”).
-de is the locative case marker meaning “at,” “on,” or “in.”
So saatlerde literally means “at the hours/times,” i.e. “at those times.”