The main issue is the definition of surprise for perfectly rational entities. Your argument doesn't really add much as you can just fix that time of day when all executions occur, and you've just restated the paradox.
The main issue is not the definition of surprise. The main issue is given to you plainly: the prisoner's reasoning is wrong.
I encourage you to give an example where the execution times are changed and I guarantee you it will suffer from the same assumptive traps as the original "paradox".
I encourage you to give an example where the execution times are changed and I guarantee you it will suffer from the same assumptive traps as the original "paradox".