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.
Click bird inside the postbox
Complete all achievements
Play all the music notes
Complete Chapter 5
Break all the pots
Open all the windows
Complete Chapter 4
Input 1915 on the safe
Turn off the Radio Tape
Complete Chapter 3
Eat all of the ice cream on Owl's side
Finish the Tea Time with Eda and Owl
Complete Chapter 2
Complete Chapter 1
Tidy up Eda's room
Open the curtain
Break all of the tombstones
Complete Prologue
Play twinkle twinkle little star in the piano
Look at the photo inside the drawer