Change cell value at certain times with javascript

I can't find any resources to learn how to do this and I'm not very experienced with js

I have a table and I need one cells value to change at certain times

    Subject1
    OK
    11:30

id='t1' is 11:30 but could be any time, I need td id='s1' value to change to 'Begins in two hours' at 09:30 (two hours before whatever the value in id='t1' is) then I need it to change to 'Begins in half an hour' at 11:00 then change to 'Closed' at 11:30

What is the best way to accomplish this, everything I have attempted so far has turned to dust. I think I need a better plan of attack but haven't found any relevant references. Is javascript the wrong way to attempt this? Please assist.