HTML page that changes text during a specific time and date using JavaScript

I am currently making a website that shows what time the current class will end for school. For example if the current class period (Period 1) ends at 10:30 and it's 10:00AM the page would dispay that the class ends at 10:30AM, but if the time were 10:31AM it would display the ending time for the next period (period 2) is 11AM. I have found that this is a simple idea but I don't know how to describe it so it will make complete sense. I am a begginer in JavaScript so I need somewhere to start, some sort of template, then I would be good, thanks.