If you have been locked out of your yahoo account for one reason or the other, like entering a wrong username / Yahoo ID or password more than 3 times. You have to be aware that Yahoo protects your account from unauthorized access by restricting time the periods (number of times) when you can use your security question to change your password. Your questions will be locked for 24 hours if you have accessed your account recently and there was also an attempt to receive a password using the security questions. Don't get scared because you can still have access to to your mail and all the messages in it, all you need is to have patience for 24 hours before you can try again.
Immediately After the 24 hour lock, you can make another request to use your security questions to reset your password using the Yahoo Password Helper at https://edit.yahoo.com/forgotroot/.
Do you Have an alternate email address or a mobile number associated with your Yahoo account? Try to reset your password first using your alternate address at https://help.yahoo.com/kb/alternate-address-sln2047.html with the link on your mail or mobile number at https://help.yahoo.com/kb/mobile-number-sln2694.html with the security code sent to through SMS Text message.
NOTE: If you didn't try to reset your password recently using your security questions? You should immediately change your password at https://help.yahoo.com/kb/password-sln2035.html to avoid your yahoo account being hijacked.
Check out the Yahoo Security Center at https://safety.yahoo.com/ for a full rundown on account security and ways you can protect your account.