Exactly. "Early" is generally understood to mean before the "time in question" -- the time that serves as the frame of reference when an engagement will occur.

Exactly. "Early" is generally understood to mean before the "time in question" -- the time that serves as the frame of reference when an engagement will occur. Asking participants to arrive early would, at least to me, strike as a caveat to those who might otherwise arrive late -- but not at the "time in question". On time is on time, which is AT the stated time. Not before, not after.