It’s hard to say what days get more queries because we get so many every day. I’d estimate that Mondays and Fridays are the busiest days, but that’s just a guess.
What’s more interesting: queries don’t stop coming on the weekend.
Weekends are when not to submit. Agents work constantly, but family time is nice now and again. We’re human too.
Knowing that, you might slip your query in on Friday and give us our weekend.
But. Monday I’ll return fresh and excited. I don’t know whether that affects how I respond to queries, but I still recommend you query Mon-Thurs. You have the smallest chance of catching an overwhelmed agent.