Hourglasses scattered across the map

[RED_DENAMITE]

What are they for or what do they activate?

[Zackoto]

its the collectible dogs for those who bought the "dlc" version
the free version replace them with simple hourglasses

[Eren Hinger]

If you buy the Supporter Edition, they will turn into collectible dogs that unlock stuff like concept art, level design, developer commentaries, etc.