Yes. Making my comic, I absolutely could not finish a page in five hours.
And look, I planned a detailed comic because that's what I want to make. Under normal circumstances I do a page a week (though I work in batches so it's not quite that straightforward). But if I was suddenly crammed into a five hours a week schedule I would no longer be able to make the comic I want, or I'd have to opt to take longer. I'd opt for the latter, personally.
I just reject the blanket statement that everyone can do X in Y time. It's based only on what works for you. It ignores and dismisses the realities of other people.
And again, to be clear, I'm all for encouraging people that yes, they can find time to work on a comic. If they're just starting one? Absolutely encourage them to consider time management, and what they can get done in a week.