There are 22 time capsules in total.
They are audio recordings which play back upon collection.
Below is a list of their number as displayed in your data menu and all of their locations.
Time Capsule 01
Appearance: Envelope
Location: Level A-2 - Visible from the spawn.
Time Capsule 02
Appearance: Beachball
Location: Level A-4 - From the spawn go straight head until you see it.
Time Capsule 03
Appearance: Scroll
Location: Level A-5 - Behind a ruined wall close to spawn.
Time Capsule 04
Appearance: House with a family inside of it
Location: Level A-7 - Upon warping in to the area turn right and you'll see it.
Time Capsule 05
Appearance: Hourglass
Location: Level B-2 - Clearly visible to your right when exiting 'Moonshot'.
Time Capsule 06
Appearance: Writing Quill
Location: Level B-4 - In front of the Sphinx.
Time Capsule 07
Appearance: Pyramid
Location: Level B-7 - To the right of the entrance to "Big Lump of Mine".
Time Capsule 08
Appearance: Sputnink
Location: Level B-7 - Close to the entrance of "Bouncing Side By Side".
Time Capsule 09
Appearance: Ouroboros
Location: Level C-1 - From spawn in go straight head past the terminal and head slightly left.
Time Capsule 10
Appearance: Cog
Location: Level C-3 - Left of the spawn.
Time Capsule 11
Appearance: Telescope
Location: Level C-5 - Looking straight out from the entrance of "Dumbwaiter" you will see it in an archway across the path.
Time Capsule 12
Appearance: Hand Mirror
Location: Level C-6 - Right next to the statue of two dragons resting.
Time Capsule 13
Appearance: Controller
Location: Level C-7 - From spawn it is ahead of you and on your right immediately within view.
Time Capsule 14
Appearance: Handcuffs
Location: Level C-7 - Turn right from the entrance of "Carrier Pigeons", it will be obscured by walls.
Time Capsule 15
Appearance: Crib
Location: Messenger Island C - Close to the messengers tomb.
Time Capsule 16
Appearance: Harp
Location: Messenger Island A - Near the Fan that takes you to the Messenger's Tomb.
Time Capsule 17
Appearance: Hammer
Location: Messenger Island B - Behind the Messenger's Tomb enclosure.
Time Capsule 18
Appearance: Sphynx
Location: Tower Floor 1 - Turn left as you exit the elevator.
Time Capsule 19
Appearance: Tombstone
Location: Tower Floor 2 - Facing the puzzle entrance, the second purple field, turn left.
Time Capsule 20
Appearance: Double Helix
Location: Tower Floor 3 - After the Red Sigil Puzzle gate.
Time Capsule 21
Appearance: Computer Chip
Location: Tower Floor 4 - Left of the entrance to the puzzle area.
Time Capsule 22
Appearance: Skull
Location: Tower Floor 5 - After the Red Sigil Puzzle gate.