On average how long does it take to hear back from MEPS on a medical read?

Up to 4 business days. USMEPCOM Regulation 40-1, paragraph 11-4.

Rule of thumb is 1 business day per page and it all depends on what the med read is for. I’ve only seen it once where a guy had 150 pages and it came back in like 3 weeks. That’s a rare case. For my center at least.