Here is the full list of all 20 When The Past Was Around achievements. It takes around 2-3 hours to unlock all of the achievements on Windows.
Open all the windows
Complete all achievements
Eat all of the ice cream on Owl's side
Click bird inside the postbox
Break all of the tombstones
Play twinkle twinkle little star in the piano
Play all the music notes
Complete Chapter 5
Break all the pots
Complete Chapter 4
Input 1915 on the safe
Turn off the Radio Tape
Complete Chapter 3
Finish the Tea Time with Eda and Owl
Complete Chapter 2
Complete Chapter 1
Tidy up Eda's room
Open the curtain
Complete Prologue
Look at the photo inside the drawer