Even if an agent has fast response times on QT, it's customary to wait until the time stated by the agent has passed. Worst case scenario: The agent put you in their maybe pile, you nudge too early, they think you're impatient and ignored their response time and decides they don't want to work with you based on that. Granted, that won't always happen but I'd think, just in general, nobody wants to be "that person".
Queries do end up in spam folders (has happened to me) and queries are missed, but maybe piles exist and sometimes agents just want to take a second look. Publishing isn't a fast industry and Covid has made it even slower. Nudging is perfectly fine and acceptable if an agent hasn't replied after the time they stated on their website/the agency website, but I wouldn't recommend ignoring query guidelines.