How to set default value to the field based on selection and the field is also can be editable.
E.g. If I choose work Location as office the field will set default as 8 hours and it can be editable in case the employee is on vacation/training.
Use the set value rule on your hour-field and update the field after a selection happens in your location field.
Unfortunately responsive forms can only handly set value rules for text fields. But the upcoming universal forms that will be launched soon will be able to set almost every type of field without using JavaScrip.
Hope this helps.