How long is it supposed to it take for antibiotics to start working for a toothache?

12-24 hours: ...But an antibiotic may not work at all. If the infection is inside of a tooth, for example, the offending tooth will require treatment.

Soon: Antibiotics usually start working right away, but you might not have any pain relief for 24-72 hours, depending on the infection.

More info needed...: Are you infected? Do you have an abscess? If not, then the antibiotics are useless. Regardless of the cause, you'll need to have a local dentist evaluate and treat that tooth. Please call for an appointment.

See a dentist: You must treat the source of the infection, not only the symptoms. Therefore, you need to clean out the inside of the tooth to remove the bacteria which is the source of the infection. The antibiotics cannot reach the source of the infection. Ask your dentist for more information.

By next day: Usually by next day. Antibiotics don't always work. For cure, see DDS.