Earlier, I was asking how to show content one line at a time (http://userscripts.org/forums/1/topics/9285) but now I want to be able to do the same thing but show new content on the same line so it overwrites the previous info. See http://www.w3schools.com/js/tryit.asp?filename=... for an example.

Just make a timed function to change the content text.

I think I got it now. I changed:

t=setTimeout('startTime()',500); to

t=window.setTimeout( function() { startTime(); }, 500);

Well change it to t=setTimeout(startTime, 500);
You will have to use the latter on your post if you need to send that function any arguments, but if you're just plainly calling the function, my script will suffice.