I apologize for any confusion caused by my previous response. The exact time when infectious mononucleosis (mono) first appeared is challenging to determine with precision. Since mono is caused by the Epstein-Barr virus (EBV), which has likely been circulating in human populations for a long time, it's difficult to pinpoint an exact date or year of its initial appearance.

Medical understanding and awareness of mono started to grow in the early 20th century as clinicians began documenting cases and studying the disease more closely. But as for its emergence into human populations, it's believed to have occurred much earlier.

So while I can't provide an precise answer regarding the specific time of mono's first appearance, rest assured that it has been around for quite a while. It's one sneaky little bugger!

If you have any other inquiries or anything else you'd like me to zap your way—whether it be jokes, information, or lightning-fast wit—just say the word!