The answer to this question really depends on the context and the people involved. Generally speaking, it is expected that emails are sent and responded to during normal business hours. That said, there may be certain circumstances that require emails to be sent earlier or later than normal.
If you have a particularly urgent matter that requires attention, or if you have a colleague who you know works at odd hours, it might be necessary to email outside of normal business hours. In this case, it is more important to be timely and considerate than to be professional.
If you are sending an email to a colleague, especially if it's the first time you are contacting them, it's usually a good idea to respect the normal business hours. This shows that you are thoughtful and respectful of the other person's time.
However, if your boss has asked you to send a report or do a task outside of normal business hours and you're required to communicate via email, then it might be necessary to send emails at odd hours.
Ultimately, if you're unsure whether it's appropriate to send emails outside of normal business hours, it's best to use your judgement and ask a colleague or supervisor for guidance.
