On the third day after Headmaster Eugene and Headmaster Mumford visited Abel, he came out of the Dark World early in the morning because he was just a step away from being fully fulfilled.
As his power grew, he could not neglect the power of law, and he wouldn't take a risk leveling up in the Dark World.
As for that sea turtle shell, he thought about giving it to Doff, or his summon, but finally, he gave it to his crystal angel statue.
In the special dimension, that shell began to transform with faith at a much faster rate than Doff's kingdom, or his god rank summon's worlds.
But still, it could take tens of years until the crystal angel statue's energy fully consumed the shell.
Even if you considered the time differences in the Dark World, it could take 2 to 3 years in the Central continent.