Learn Portuguese (Portugal): Abrimos a loja cedo.

In Portuguese, you often don't need to use the subject pronoun like nós (we). The ending of the verb already tells you who is doing the action. Since abrimos specifically means 'we open', adding nós is optional and usually left out in natural speech.

Could abrimos also mean 'we opened' in the past tense?

Yes! For regular verbs ending in -ir like abrir (to open), the 'we' form is exactly the same in both the present tense and the simple past tense. You just rely on the context of the conversation to know whether someone means 'we open' or 'we opened'.

Would cedo change its ending if we were talking about multiple stores?

No. Cedo (early) is an adverb, which is a word that describes when an action happens. Unlike adjectives (which describe nouns and must change to match masculine/feminine and plural/singular forms), adverbs never change their spelling. It will always be cedo.

How would I say the opposite: 'We open the store late'?

The opposite of cedo (early) is tarde (late). To say 'We open the store late', you would simply say Abrimos a loja tarde.