How long are account verification emails and password reset emails valid?

Question

How long are account verification emails and password reset emails valid?

Answer 

Both account verification emails and password reset emails expire after 24 hours. The verification email can be resent to the user, and the user can also request a new password reset email after it expires.

When the account verification email expires, the user receives an error such as "No user found (invalid activation link)" as shown here:

When the password reset email expires, the user receives an error such as "You can generate a new reset link from the sign-in page" as shown here:

If you are having issues receiving one of these emails, see: I am not receiving my password reset email...