Here is my 100% achievement guide with timestamps :)
Hope this helps
Intro - 0:00
1. Queen Of The Swings - 2:05
2. Once The Greatest Of Concerns - 3:20
3. Adieu, My Little Tree! - 4:40
4. A New Tree & Leaf 1/5 - 6:10
5. Change The Channel! - 6:55
6. This Is How It Begins - 8:25
Leaf 2&3/5 - 9:40
7. Lobel Prize! - 10:45
8. Heard It All Before - 11:50
9. Shut Down, Roundybot - 13:15
10. Sh! This Mission Is Secret - 15:05
11. First Of Her Name - 18:50
Leaf 4/5 - 20:05
Leaf 5/5 - 20:20
12. A Tree Reborn - 20:45
13. This Mission Is... Failed - 21:15
14. The Sound Of Hope - 23:00
15. If There's A Will... - 26:00
16. All Is Lost - 28:50
17. My CPU Is A Neural-Net Processor - 32:15
18. This Is The End - 33:50
19. A Brand New Day - 35:40
20 & 21. Leafless & Everything's Alright (Do NOT Skip The Credits) - 42:50