Yes, you can say "Good evening" at 10 PM. In most cultures, "Good evening" is generally used as a greeting in the evening hours, typically starting from late afternoon and lasting until around midnight. While the specific time when "evening" begins and "night" starts can vary depending on cultural norms, 10 PM is still considered part of the evening.
Using "Good evening" at 10 PM is appropriate and polite, especially in formal or semi-formal settings. However, it's important to consider the context and the person you are greeting. For example, if you are meeting someone in a very casual or informal setting, a simple "Hi" or "Hello" might be more common and appropriate. But if you are attending a formal event or speaking with someone you don't know well, "Good evening" is a respectful greeting at 10 PM.