need to know how many miles before I have to do a timing belt replacement

I would change it around 60,000 mi

I have about 260k miles on my 1999 4Runner. I changed it the timing belt the first time at 80,000 miles and then again at 200,000. The times when I changed it, There were no cracks and very little signs of wear. I plan to change the timing belt again when I hit 300,000.