Seems like simple requirement that can be done using workflow, but I am having second thoughts that it might not work.
So I am thinking to create a dateTime field to store Start Time when case entered Open state and In workflow check the difference between Now() and this start Time field and if it is more than 24 Hrs then send email.
But my doubt is workflow will only fire if record is edited, which is wrong. I need to keep checking the difference of Now() and Start Time & as soon as it reaches 24 send email.
Is it even possible using workflow or process builder? Or Apex is the way to go?