I'd say that's excessive. An hour max would be more reasonable otherwise you're just creating a discouraging workplace. Note that would be an hour of real effort though, not half arsed googling. Making a genuine effort is more important than the time taken.
The amount of time is entirely dependent on what kind of work it is and what kind of blocked you are. Can’t get your build to succeed? Ask for help quickly. Can’t get your research model to produce useful results on the first try? Maybe try a few things first.
Yeah, it's a bit disheartening to hear some (presumably) experienced people advocates for never allowing the junior to dig and deal with things on their owns.
I can imagine the scenario where a build fail due to some missing incantations that needs to be invoked, and sure, you shouldn't spend more than 15 minutes on trying to resolve it. But that should be rare, while the common blockers for junior tend to be their lack of understanding in even bog-standard systems and situations (why can't system X do Y, why did person Z require A). In those cases, part of the expectation when assigning them the work would be for the junior to learn those on their own.