Congrats on the full request!
I would echo what has been said here and say better to query only a few at a time so that you don't run through all the agents you have. It's also just less confusing.
Personally, I'm only querying one agent at a time for maximum result. Every time I fail it's back to the drawing board and I make changes. The Query Critique board on here has been of immeasurable help.
My most recent rejection, the first agent I queried for this memoir, responded with an hour and a half to an email query. That satisfied me a great deal. I would rather know, and soon, even if it's a rejection.
What is the longest one should wait before continuing? I will have to check my inbox, but when I started sending out my first query, I think I sent to about 5 agents, but only 2-3 replied back. This was about 4 years ago, so obviously the non replies are rejects (or got lost in the mail). Now that I am ready to start submitting again, I'd like a time frame to consider either tweaking my query again or moving on to another agent.