Here are my most recent query stats, for anyone new to querying. In early 2021, I queried 109 US agents and 11 non-US agents.
Of 109 US agents, 57 did not reply. 52 replied with form and personal rejections. It took from zero days (three agents) to 250 days for those Rs to arrive. (One full request.) That's an average wait of 53 days, with a standard deviation (FWIW) of 60 days. (No response from just over half of the agents queried.)
Of the 11 non-US agents, 6 did not reply (again, just over half). The other five were rejections, three form and two personal, and it took between 28 and 180 days to receive those. That's an average wait time of 81 days, StDev of 60 days.
These numbers are in line with the querying stats on my first project, queried 2019, although there were quite a few more personal Rs this time around. (Fewer full requests, which I expected, in part because I would not personally ask for a full on a second-in-series, even if it stands alone which this does.)
I also was unsurprised (largely unbothered) by these numbers due to the request rates on Querytracker. Many agents who represent my genre request only a few percent (if that) of the queries they receive. My single full request came from an agent who requests at a higher rate. A friend of mine queried at the same time as I did, and he received replies (rejections) from agents who never got back to me at all--read into that whatever you will.
The best advice I would give my younger self (who wanted advice and tried the route of query-in-small-batches) is to identify lit agencies with a rapid response time, and query those agencies first. Because otherwise, waiting for feedback on your query means waiting months and months and months... before you send off that second batch of queries.
My second piece of advice (to my younger self, and anyone else who might be interested) is to look at the Pitch Wars showcase. Analyze the query hooks and opening 200 words, especially in your genre. See what your personal response is to those words, whether you want to read more or not, and ask yourself why. Then look at your own opening in comparison. And also see how many agents felt as you feel about the Pitch Wars entries--which you can see by the request stats.
But in the meantime--to anyone querying for the first time--congratulations on making it this far! It's a huge accomplishment.