How long does penicillin treatment take for tooth infection?

Varies. It takes about 24 hours for the antibiotic to begin working and it may take a few days for swelling to go down. Sometimes additional or different antibiotics have to be used if the first one didn't help. However, don't think that an antibiotic alone can fix the problem. It may make symptoms better, but you need to figure out why there is infection.
Typically 48 hours. It typically can take up to 48 hours for most antibiotics to reach therapeutic effect in most people.