Received injection of rocephin (ceftriaxone) and prescribed antibiotics. should i wait until next day to begin antibiotics?

Not necessarily: It depends on the antibiotic you were prescribed. A rocephin (ceftriaxone) injection lasts 24 hours so if the antibiotics prescribed were in the same class as rocephin (ceftriaxone) but just in oral form then wait until the next day. If the antibiotics were in a different class, such as doxycycline, then that should be started immediately. If you aren't sure then you should speak with your pharmacist and they can clarify.

Follow instructions: Follow the instructions of the doctor who prescribed the injection and oral antibiotics. If one does not recall the instructions, one generally can go ahead and start the oral antibiotics (instead of waiting until the next day). This usually works fine, because the level of oral antibiotics in the body will be rising as the level of injected antibiotics is going away.