I've found an olde page that I wrote many moons ago that does this - one good thing about it is that if you have 4 different URLs, the script counts those 4 and chooses a number at random between 1 and 4. If you have 14 URLs, it's a random number between 1 and 14.
I've seen other scripts where you had to insert the URLs, count them and then manually enter their total. Pah!! Amateurs!!
Save what you see here as an html page >
http://www.stevie21.com/AB/redirectCode.html
All you need to do is insert the time delay