When should I renew my Non-B visa before it expires in Thailand?

Hello everyone 😊

I'm holding one year extended Non b, and about to sign a new contract with the same school for the next two years... Current extension is expired on 31th of March. Have to go to Chaeng Watthana to get another one.

Question: Someone told me that next stamp should be done 10 days before expiration, which means 21th.... Is it true?

Thanks for sharing your experience!