As of November 2020, the Minecraft wiki's documentation of mechanics relating to turtles and turtle eggs was incomplete. I have done some digging through the code to try to understand and document the mechanics better.

Reference source code generated by MCP-Reborn (1.16.3).

Findings

Key:
⬜️ Already documented but included in this document for completeness
🔹 Partially documented on the wiki
🟢 Undocumented on the wiki / new mechanic "discovery"
⚠️ Possible bug / unintended behavior

Heartfelt note to Mojang: Please don't patch any bugs / unintended behavior :) Quirky mechanics can make the game a pleasure to play and explore.

Turtle Eggs

Trampling

• 🟢 Turtle eggs have a 1/100 chance per tick of breaking while being walked on. The egg can't be broken while crouch-walked on. [TurtleEggBlock.java:41]
• 🟢 Turtle eggs have a 1/3 chance of breaking when a living entity falls onto them. Chance of breaking is not dependent on the heigh from which the entity falls. Zombies can't break eggs by falling onto them. [TurtleEggBlock.java:47]
• 🟢⚠️ When an anvil is dropped onto a turtle egg, the anvil breaks and the turtle egg is unharmed.
• ⬜️ When a multi-egg block is trampled, one egg is broken at a time. [TurtleEggBlock.java:58]
• 🟢 Turtle eggs can't be trampled by bats - bats are explicitly called out in the code. Possibly the result of a hilarious bug report? [TurtleEggBlock.java:148]
• 🟢⚠️ Despite special handling being added for bats, other flying mobs can technically trample eggs. I have confirmed this behavior in the case of bees.
• 🔹 Other mobs like cats can trample eggs too, although it would seem that a cat would tread carefully over the delicate eggs.

Hatching mechanics
This was the big unknown I was trying to understand - there was little info on the timing of egg cracking.

• ⬜️ Turtle eggs can only crack / hatch on sand. [TurtleEggBlock.java:105]

• 🟢 Turtle eggs have a chance of cracking during random ticks. Throughout the vast majority of the day, random ticks have a 1/500 chance of causing the egg to crack. There's a small window in the very early morning hours where random ticks have a 100% chance of cracking eggs. This window is defined as the time between celestial angles 0.65 and 0.69, or 03:36 am and 04:33 am on a 24-hour clock. This window lasts 48 seconds in-game.

  3/4096 per tick chance of receiving a random tick
  24000 ticks in a day and 4% of those ticks get a 100% of cracking the egg
  1 / (24000 * 3/4096 * (0.96 * 1/500 + 0.04 * 1)) = 1.357 days per crack
  3 cracks required to hatch
  3 cracks * 1.357 days per crack = 4.07 days
  

  So on average, a player can expect their egg to hatch in about 4-5 nights. [TurtleEggBlock.java:115-122]

  Simulation of hatching ~5,000 eggs:

  The median hatching time is 4 nights and 70% of eggs hatch in 5 nights. Nearly 90% of eggs hatch in 7 nights. About 95% of hatching occurs during the 48-second window at night.

Miscellaneous

• 🔹 Babies always hatch facing due south.
• 🔹 When a multi-egg block hatches, all eggs hatch simultaneously and babies are spawned at locations throughout the source block.
• ⬜️⚠️ Turtle eggs can be placed on any block even though they only hatch on sand. They can even be placed on non-solid blocks like fence posts, string, torches, or even more turtle eggs. Breaking blocks below eggs doesn't break them.

Turtles

• 🔹 Baby turtles are actively sought out and hunted by drowneds, all variants of skeletons, zombies, ocelots, cats, foxes, and wolves.

Mating

• 🟢 Turtles have no data attributes regarding gender. When mating two turtles, one turtles is picked to lay the eggs.

  • This is possibly decided by which turtle the player clicks first.

• 🟢⚠️ According to the MC Wiki, the male turtle can breed again immediately after mating while the pregnant turtle can't breed until after laying eggs. This is not actually the case. There's a bug that allows rapid infinite breeding between a single pair of turtles:

  • Mate 2 turtles on their home beech (so there's no travel time)
  • Try to mate the male again while the female is burying her eggs
  • Then the original male will begin laying eggs too (and even drop xp for successful breeding).

  Source of this behavior: After mating both turtles' "love" parameters are reset to 0 to exit love mode. However, when the female turtle starts digging in the sand to lay eggs, her love parameter is set back to 600 ticks (so there's a 30-second window to re-breed the two turtles). [TurtleEntity.java:438,477]

• 🔹 The pregnant turtle does not have to lay its eggs at its exact home beach coordinates. It can lay its eggs at a nearby sand block.

Misc

• Turtles are instead insta-killed by lightning: Float.MAX_VALUE damage is dealt to the poor thing. Thor just yeets the turtle on sight. [TurtleEntity.java:311]
• Turtles can breathe underwater forever.