Here is the full list of all 24 SkyTime achievements.
Take more than 3 minutes to complete the tutorial
Complete Round About Time within 50 seconds
Complete Fast and Chill within 70 seconds
Complete Bullet Rain within 55 seconds
Complete Frog Like Experience within 75 seconds
Complete the game
Complete Bullet Rain without being hit even once
Die in the tutorial
Destroy all the turrets in the tutorial level
Destroy all turrets in Public Transport
Destroy all the turrets in Round About Time
Destroy all the turrets in Fast and Chill
Destroy all the turrets in Bullet Rain
Destroy all the turrets in Frog Like Experience
Destroy all the turrets in Speed Run
Destroy all the turrets in Going Up
Get a turret double kill
Get a turret triple kill
Complete Car Wash within 65 seconds
Destroy all the turrets in Car Wash
Complete Speed Run within 92 seconds
Complete Public Transport within 50 seconds
Complete Going Up within 55 seconds
Complete the tutorial