Although the transition from a manhã to a tarde is always clearly 12:00 noon, the rest of the terms are used a lot more loosely in conversation.
It’s also common for madrugada to be replaced by manhã for those early hours before the sun comes up, (just like in English).
São duas da manhã! Deixa-me dormir! It’s two in the morning! Let me sleep!
Greetings by Time of Day
For each period of the day, there are distinct greetings we use when running into people:
Although in English it would be strange to use “good night” as a “hello”, or “good afternoon” as a “goodbye”, all of these Portuguese greetings can be used as either hello or goodbye. For example, after buying something in a store during the day, you could definitely say to the cashier:
Obrigado e boa tarde! Thank you and have a good afternoon!