Unfortunately, Han Sen did not have a mutant beast soul from Second God's Sanctuary, so he could not test the upgrade time of a mutant beast soul.
However, he had a rough estimate. Han Sen guessed that the blood snail took so long to upgrade because it was a beast soul from First God's Sanctuary.
Beast souls from First God's Sanctuary did not have the feature of berserk, but the black crystal added the berserk feature to the blood snail, which probably called for a bigger change to the beast soul itself. Han Sen thought that was why it took so long.
The reason that the upgrade of the holy angel was faster was probably that she had the feature of "to be involved" to begin with.
Of course, that was only a guess. He would have experiment further to test if that was true.
