I understand the 1 hour rule, it makes sense for achievements you can go back and get from chapter checkpoints. Let's say you got 3 balloons on your first playthrough, are you really telling me you can hunt around for and find the other 27 on your second playthrough in 1 hour or under? Using a guide maybe, but using guides should not be a requirement for an achievement not getting the missable flag. What if second time round you still missed a couple in the open area part and one near the end, then a third playthrough is required. Going back to snap flash the Titan I could believe you could get done in under an hour - and yet that is flagged as missable!??
I'm not the first person to disagree with
https://www.trueachievements.com/alklein92201.htm's
uncanny ability to find all 30 balloons in under 1 hour without using a guide either.
I don't like using solutions (although I enjoy writing them). If I pay for a game I like to try and find the hidden stuff the designers put in by myself, not have someone spoil it for me and tell me where they all are. I've had fun finding secrects in games since Wolfenstein 3D and Doom. There was no world wide web back then, so you either found them yourself or waited a month or so for the secrets to be published in a magazine.
But I can't say having to replay the entire game from the beginning again, and again is particularly fun because you missed a secret but you have no idea when. That is why I created a spoiler free solution, so you know when you can stop searching and move on