How long to wait between querying different MSs?

Ok, so I went through the most recent 25 pages here, and a search yielded too many unrelated posts. Please point me to a source if there's a previous thread I have missed.

I'm curious about how long one should wait between querying two different MSs if the agent list overlaps. I read somewhere that as little as a month would be ok, but since querying can be a long process, I'm wondering if it's best to wait longer. A few months, or maybe even six?

ETA: This is all speculative, and obviously would change significantly if the work queried first received a lot of interest or spawns revisions (if I were to be so lucky). Neither work is polished yet, but I'm working on revisions for two things that seem to be coming together at the same time.

Hmm. Yea. The more I think about it, the more I think I'd prefer to not have them overlap too much, partially for my own sanity. One is YA and one is MG, so I would likely want to query some of the same agencies, if not the same agents, on both pieces. After this draft, perhaps I'll take a few days and take a long hard look at which I feel is the more wonderful, more polished, more marketable work and try to focus on that one first. I would expect the various rounds of QLH and query sending may take quite awhile.

On the upside, it might buoy my spirits to know that if the first MS doesn't land an agent, I've already got another project I feel passionately about. (As well as give me something to focus on while querying so I don't bite my fingernails off.)

Thank you both!