When writers are often advised to send queries out in batches of perhaps ten or so at a time, it's unclear to me how long one should wait before sending out another batch. A few agents respond quickly (with a decline) but many say that they may be back in ten to twelve weeks - if they're interested.
So - that's a long time time (maybe 3 months) before sending out another batch - and we have to be open to the distinct possibility that there will be no response after that time, because the agent isn't interested.
What's the best timing on batch querying for a writer?
Ten to twelve WEEKS on a query?? Zoinks, that's really bad. I thought 30 days was the time limit on queries and twelve weeks on a full (please do not look at my stack of requested fulls--12 weeks is just a fond memory.)
Truthfully, I don't know the answer to this question because I don't send queries like you do. I get them, read them, set them on fire, and talk about them, but I don't send them. (Well, ok, I do if you count editors, but I send all those at once and assume everyone will want to buy--different ball park.)
I think the answer is more likely to be found at the place where writers hang out: AbsoluteWrite Forums. I'm not sure which thread will be useful for you, but I bet there's been a bunch of discussion about this.
And I'll also wager that the readers of this blog will have some ideas.
Readers? Let me know what you think about this. (I'll be over here reading my queries and replying in 24 hours)