Learn Swedish: Hunden har inte ätit på flera timmar. - The dog has not eaten in several hours.

We use på because the sentence is negative (inte). In Swedish, when you talk about how long something has not happened, you use på. If the sentence were positive, like if the dog had been eating for several hours, you would use i instead.

Does flera mean "more" or "several"?

Here it means "several". While fler (without the 'a') usually means "more" in the sense of a larger amount, flera is the standard word for "several", especially in phrases like flera timmar (several hours).

Why is the verb ätit and not äter?

This sentence uses the present perfect tense ("has not eaten"), which requires the helper verb har followed by a special verb form called the supine. The supine form of äta (to eat) is ätit.

Why does inte go right in the middle of har and ätit?

In a normal Swedish main clause, words like inte must be placed immediately after the first, conjugated verb. Since har is the first verb, inte steps in before the second verb, ätit.