Learn Portuguese (Portugal): Chegámos ao mesmo tempo.

In European Portuguese, the acute accent marks the past tense. Chegámos means "we arrived", whereas the present tense "we arrive" is written as chegamos without the accent. The accent also changes the pronunciation by opening the A sound.

Why do we use ao here instead of no to say "at the"?

In Portuguese, set phrases expressing a specific point or moment in time often use the preposition a. Combined with the masculine article o for the noun tempo, it becomes ao. The preposition em (which forms no) is generally used for longer periods of time like months, years, or seasons.

Does mesmo always mean "same"?

Not always! While here it is an adjective meaning "same", mesmo can also be used as an adverb meaning "really", "exactly", or "even". Because it acts as an adjective in this sentence, it matches the masculine singular noun tempo.

Why isn't the pronoun nós included at the start of the sentence?

It is not strictly necessary. The verb ending -ámos already makes it perfectly clear that the subject is "we". In Portuguese, you generally drop the subject pronoun unless you want to add special emphasis or clear up ambiguity.