Be as fair as possible
Brachylog, 12 11 bytes
My first Brachylog answer
Take input as a string
{~cĊịᵐ-ȧ}ᶠ⌋

Try it online!
Explanation:
ᶠ will find all possible outputs for the predicate in {…} and store them in a list. ~c says that the output is a list that, when concatenated, is equal to the input. Next Ċ asserts that the the output of ~c has length 2.
ịᵐ converts both elements of the output into integers (this gets rid of leading 0s), -ȧ takes the absolute difference of the two elements.
Once we have our list of all possible outputs, we get the minimum element with ⌋