Hi Joel (and everyone)-
You can't set up special hours that have adjacent 24 hour days for GMB sites*. What you can do is change your "normal" hours to 24 hours, then set up special dates for those days when you're not open 24 hours. So if your library opens for 24 hours during finals week, you have to switch back and forth.
At my previous library, I left the hours section blank on the GMB page since search engine results were correctly routing users to our hours page on the website--which dynamically pulls hours from a standard GCal. That way I didn't have to constantly remember to update the hours throughout the semester.
*You can get support from Google by direct messaging @googlemybiz on Twitter. I also mentioned to them it would be much more helpful for businesses like ours to have GMB pull hours from a standard GCal.