Learn Russian: Он дал показания как раз во время допроса. - He gave testimony exactly during the interrogation.

Yes, but it slightly changes the flavor of the sentence. Both particles mean "exactly" or "specifically." However, как раз is often used to highlight a coincidence in time or a perfect fit (meaning "right at that exact moment"). If you use именно, it sounds more emphatic and contrasts with other options: "specifically during the interrogation (and not before or after it)."

Why is показания in the plural when the English translation says "testimony" (singular)?

In Russian legal contexts, giving testimony, statements, or evidence to the police is conventionally expressed in the plural: давать показания. The singular form, показание, exists but is mostly used for the reading of a meter (like a gas or water meter) or a medical indication.

Is во время the same word as the adverb for "on time"?

No, it is important not to confuse them! Вовремя (written as one word, with the stress on the first "o") means "on time" or "punctually." In this sentence, we have the prepositional phrase во время (written as two words, with the stress on вре), which means "during" and always takes the Genitive case, as it does here with допроса.

Since "during the interrogation" implies a period of time, why is the perfective verb дал used instead of the imperfective давал?