I will respond within three weeks if interested, says literary agent Jonathan Lyons. If you do not receive a response within three weeks then....no response is a no in literary agent circles.
Three weeks is more than enough time. I've already ticked this one off as a non-responding rejection even though it's been but ten days.
If something catches an agent's eye, and that something is inevitably the hook sentence that opens your query, then you'll hear back from them right away. Within days, most often.
They're in the business of making money, and if one agent sees something in your proposal, it's possible that other agents have seen that same thing and it's all about who's first out of the gate.
For many agents, they already have enough clients. Anyone new added to the roster is filling a gap in the agent's talent stable. Maybe you've written something brilliant, but if it isn't a Regency romance set in the Yukon, which is what an editor happens to be looking for, then you'll get a rejection.
Should you, by sheer dumb luck, send your query to an agent who is looking for the subject of your manuscript, you'll be asked to send along a few pages as a sample. Not only does your query have to fit a particular set of requirements, but you have to tell your story in a way that meets some preconceived needs. Hit on all points and there's a chance for you.
Hitting all those points is unlikely. Hence, it's almost impossible to land an agent and a publishing contract.
Don't waste time wondering if a non-responding agent might be considering your query after two or three or more weeks have gone by. Move on. Revise the query, personalize it for the next literary agent on the list, but don't wonder if that wonderful agent just might respond in four weeks.
Interest is demonstrated in haste. It's the rejecting that's plodding.