Query tracker stats and my own experiences so far is that agents respond VERY quickly if interested. Not always, but many do. (Qt shows you how quickly people record responses and where you are in a queue.)

And it makes sense. If you see a hot project, you leap on it. Or you lose out to faster agents.

The consistent trend I'm seeing is faster agent responses overall, but at the expense of No Reply Means No now being standard.

Unless the agent consistently takes a month to reply (some British agents do) then I write them off as CNR after two weeks. On average.