How long before my non-B extension and work permit renewal should I start the process in Thailand?

Your stamp is already less than 30 days, so you should be able to apply for a new yearly extension anytime now.

Most offices set 30 days until the due date as the application period, and a few such as Bangkok, and Chiang Mai set 45 days.

Some offices set shorter application periods for tourism extensions, but I'm not aware of any office setting less than 30 days limit for Non-Imm type extensions.

Talk with your school/employer as soon as possible. Don't wait until the last minute. You may need to renew your work permit first and then apply for a new yearly extension. If that is the case, you cannot get them done in one day.