If someone sends you a message saying, "Good night, I'm going to bed now, I'll talk to you later," it's generally courteous to respond, but whether you need to reply depends on the context of your conversation and your relationship with the person.
Here are a few considerations:
Close friends or family: If you are close to the person and have been having an ongoing conversation, it's polite to respond with a simple "Good night, sleep well!" or something similar. It shows that you acknowledge their message and care about their well-being.
Casual conversation: If the conversation was casual and not particularly important, it's still nice to acknowledge their message with a brief response like "Sure, good night!" or "Talk to you later!"
Formal or business setting: In a formal or business context, a response might not be necessary, especially if the conversation had reached a natural conclusion.
Late at night or if you're busy: If it's late at night or you're busy with something else, it's okay to reply later when you're available, or even the next day, with a message like "Good night, sorry for the late response. Talk to you later."
Remember, responding to a message like this is more about showing politeness and consideration than it is about obligation. It's a way to maintain a positive and respectful communication flow with the other person. However, if the conversation had already concluded or it's clear that they are going to bed and don't expect a response, you don't need to feel pressured to reply immediately.