Learn Hardcore Russian: Пора вернуться домой, пока не начался дождь. - It’s time to go back home before the rain starts.

Пора is a predicative word (a “category of state” word) meaning it’s time. It often forms an impersonal sentence, so there’s no grammatical subject:

Пора вернуться домой. = It’s time to go back home. If you want to specify who, Russian commonly adds the dative:
Мне пора вернуться домой. = It’s time for me to go back home.

Why is вернуться an infinitive, not вернёмся or я вернусь?

After пора, Russian normally uses the infinitive to express a general necessity/rightness (“time to do X”):

Пора + infinitive is the default pattern. Using a finite verb would make it more like a decision/plan:
Пора вернуться домой. (It’s time to return.)
Вернёмся домой. (Let’s go back home / We’ll go back home.)

Why is it вернуться (perfective) and not возвращаться (imperfective)?

Вернуться is perfective and focuses on the return as a single completed event (getting back home).
Возвращаться is imperfective and focuses on the process or a repeated/ongoing action. Compare:

Пора вернуться домой. = time to (get) back home (result).
Пора возвращаться домой. = time to be heading back / start making your way home (process).