The resolution doesn't actually mention leap hours, just that the delta is allowed to grow up to one hour. What should happen then is to be decided by future generations.
A century later we'll finally be able to fix Earth's orbit to make a nice round 360 days per year, 12 months of 30 days, nice and clean, no more complexity or confusion... ah, that'll be the day.
So the example given Feb-31 is stored as 1 month + 30 days past the start of the year and would trigger right on time march 2nd or 3rd, depending on leap year. In fact I started doing it to handle birthdays on leap day, there is not always a February 29, but there is always a day 29 days after the start of February.
* https://leginfo.legislature.ca.gov/faces/codes_displaySectio...