How do relics work exactly?

[MabinoZerk]

I've collected quite a few, but I don't remember what you're supposed to do with them.

[(Edgy) Asriel Dreemurr]

There are stands around the ship that you repair with pons, and then place the relics on them. When you complete a relic it unlocks the purple time rift for a world.

[FibS]

Relics are sets of 3~4 pieces that must be assembled on one of the four (5 with StD) stands around the ship. The stand you choose determines which level gets the resulting unlocked Time Rift.

• 2 in the main ship room (left Ch. 1, right Ch. 2)
• 1 in the gallery (Ch. 3)
• 1 in the science room (Ch. 4)
• [StD] 1 in the laundry room (Ch. 5)

Once you have every Relic, all further relic pickups will be Rift Tokens.

[snoopeebaron]

If you collect a couple of relics, stack them all up and they are up for display, along with a purple time rift for the level!

[E3kHatena]

You have to stack relics in the right order on the shelf to unlock Time Rifts. So the top half of the burger sits on top of the bottom half, etc. I will note that the cow relic requires you to start with the UFO first, I stacked all the cows up and then put the UFO on top and never understood why I was one Time Piece short going for 100%.