Reader (the Notorious) C.L.G. tagged Otto on a Facebook rant (the only kind that matters):
[Something] that just made me cringe during a meeting: “She was able to get back to me timely.”
She then continues: I…completely refuse to use “timely” as an adverb. It may look like an adverb, but NO, it’s an adjective. NO NO NO NO. “A timely response” is OK. “Responding timely” is NOT OK. (And while it would be fun to say, “Responding timelyly” is not ok, either.)
A future Lexicide editor in the making, no doubt.
Neither Otto nor Lex have ever heard or read timely used as an adverb, and neither had any of CLG’s compatriots. So I looked it up. Bad idea.
I found a 2007 article where Lynn Gaertner-Johnston, flummoxed by the same awkward construction, did the same:
Consulting my American Heritage College Dictionary, I learned that timely is also an adverb meaning “in time” or “opportunely.”
Merriam-Webster agrees. Timely can be an adverb. But as a wise leader once said, just because one can do a thing, it doesn’t follow that one must do that thing. Please observe Lexicide and Safire’s maxim that if a word usage is ambiguous, choose another word. Promptly, opportunely, and the easily understood on time all work quite nicely.
— Otto E. Mezzo
See also: Timeous, which includes a further admonition that the use of timely as an adverb is archaic and likely to get you laughed at.