The agent submits and the agent gets the answers. It's entirely possible for the agent to submit to several houses and wait till all the answers are in. You should periodically (maybe once a month) get rejections, but you won't hear of an acceptance until the phone rings.
I cannot answer your question, because much depends on when the agent starts submitting (timing may be important), but I've often had to wait 6 months or longer. Acceptances for me always came in the spring.
Michael it varies. It can be as soon as an hour (yes some agents hear back from editors that quick) or can be up to a year or more. Yep, even with an agent. The agent will keep checking up but that doesn't mean the response is gonna be faster.
That's why it's best to just work on other things and not concentrate on time frames because it can drive you crazy.
I have several author friends right now with agents where houses have been sitting on their work since the beginning of the year or more.
Think of it like this, sometimes not hearing from an editor is a good thing because it might mean some deals are being talked about. It only takes a second to be rejected but it takes a while longer to get a deal.
It took about two months for my publisher to respond favorably -- but another six months until the contract was finally signed. The acquiring editor had to get approval from the company president, who was travelling a lot, and there were other hoops to jump through. I really had to learn to be patient -- not my strong suit by nature. My agent almost strangled me a couple of times...
My agent works like IJ's. I normally don't hear about individual rejections, although I did hear last month that one big NY publisher passed my manuscript around internally for 14 months and then said no. She was not happy. Don't know where Austin Carr is off to now, but that's the way I want it. I write them. She sells them. It was our handshake deal from the start five years ago.