Hello, if you spot a tick and you develop a bulls eye rash but no other symptoms of lyme, how long is the initial treatment period of antibitics?

14to21 days. With history of tick bite and bulls eye rash called erythema migrance, treatment with antibiotics like doxycycline, or amoxicillin, or cedtrixone is for 14to21 days according to cdc guidelines.
Treatment Varies. The disease you are referring to is lyme disease which classically presents with a bulls eye rash. Generally, for lyme disease without other symptoms antibiotics are taken for 14 days. Symptomatic treatment lasts from 21-28 days. Each case is different so speak with your doctor.
7-14days. If you develop rash, fevers, or other symptoms, 7-14 days of Doxycycline is the recommended treatment . http://www.cdc.gov/mmwr/preview/mmwrhtml/rr5504a1.htm.