General help

There is likely not to be a setting for it, but what you may be able to do is to setup a cron job for it. Start with the Moodle Docs on cron. Set up a cron task that allows it to alter enrollment plugins after checking the closing date of a course. I have no idea how to do it, but if you have some skills at programming, you can work it out. You may find a better answer in the Developer's Forum. 

It's a very specific requirement. I can imagine that we're in the realms of developing a custom enrolment plugin to do this.

I know of no automatic setting, but you could easily remove self-registration yourself a day before the course expires. I don't do this, but if I were to do it, I would put a reminder in my calendar so that I would not forget.

So, are you saying that you do want to allow a student to self-register 25 hours before the course ends, but not 24 hours? Your question makes me wonder what you are trying to prevent.