I earned this achievement today. This is to offer some advice for an efficient strategy to reach full completion of Quantum Break.
1. Begin the game on hard and systematically collect every item and every chronon source as you go along. Check your timeline often to see if you passed something and re-load checkpoints if needed to go back and find them.
2. Do not change any junction decisions until you have earned every collection achievement.
3. You can go back and replay timelines on easy to get anything you missed once you finish the last Act.
The collections change if you change your decisions at the junctions. This means you may not maintain 100% collection in timeline during a replay. Not a problem if you have earned every collection achievement before you make a different choice during a junction replay. This means you leave the optional junction choice achievements until LAST, which is what I chose to do here. Also may not be a problem if you reload a checkpoint to get another junction choice BEFORE moving on to a next Act/chapter. But if you want to read the alternate choice intel, etc. then make alternate junction choices after you have completed all the collection achievements. This way you can re-play anytime and read the alternate choices material and experience the choice differences in-game.
BOSS FIGHT: I went into the boss fight under powered and after a couple months off the game. It was frustrating until I learned to watch for the red/orange ball shaped bombs and get proper distance away and know what cover was needed where and when. Learned to use the spawning boss bombs to kill enemies. (The bombs spawn about every 10-12 seconds). Had to relearn proper power management and get the attack timing right to avoid death by bombs spawning on me. Needed some lucky enemy placement spawns. Also multi-group attacks helped. Needed to run and strategically use cover while planning out my paths of travel and enemy avoidance vs. engagement. Since I got all collectibles in last Act before boss battle, and since I played in hard mode, I did not have to replay it once I beat him!
A great game and now I am set to replay and read the alternate junction choice material without the stress of achievements not unlocking.