Hook on change

Is there hook that will trigger when a custom post type (ACF) is changed, but before it is published?

Reason is that I have two date field and I would like to auto fill the second one with a calculation on distance and speed. So when user add distance and speed and the start date the end date is automatically filled. And how would you go about to do this? Or push in the right direction, new to the whole wordpress programming.

Thanks