Learn Turkish: Saat on ikiyi beş geçiyor, spiker neden reklamları okuyor? - It is five past twelve, why is the announcer reading the advertisements?

When telling the time by saying it is "past" an hour, Turkish puts the accusative case ending on the hour. You then add the minutes and the verb geçiyor (passing). It literally means "it is passing twelve by five."

Could I use var instead of geçiyor for this time format?

You use var (there is) when saying it is minutes "to" the next hour, which requires the dative (direction) case. For example, "five to twelve" would be on ikiye beş var. Because this sentence says "five past twelve", we must use the accusative case and geçiyor.

Is spiker just the English word "speaker"?

It is a loanword borrowed from English, but its meaning is narrower. In Turkish, a spiker specifically means a broadcaster, TV news anchor, or radio announcer, not a piece of audio equipment or a general person who is talking.

Why does reklamlar end with an -ı here?

That is the accusative case ending again, but this time for a regular direct object rather than for telling time. Because the announcer is reading specific advertisements, reklamlar (advertisements) acts as the definite direct object of the verb okuyor (is reading) and becomes reklamları.