How do I adjust baking time ? Recipe calls for 8” round springform and I only have a 9”?

Alice Medrich, an old pro who is full of useful knowledge and generous in sharing it, addresses just this point in an article posted here on Food52. It's an excellent resource on adjusting pan sizes, the impact on baking time, etc. Here is a link: https://food52.com/blog/13239-how-to-make-your-baking-recipe-fit-your-pan-size

Quoting from the post is this of particular relevance:

"Just by glancing at the two pans, you might think that a 9-inch pan is very close in size to an 8-inch pan of the same shape, thus making it a reasonable substitute. But if you check the chart, you’ll find that a 9-inch square pan is more than 25% larger than an 8-inch square pan. (The relationship between a 9-inch and 8-inch round pan is similar.) Such a considerable difference will result in a 9-inch batch of very thin brownies that may be over-baked by the time you check them for doneness (because thin brownies bake faster than thick ones). Knowing this beforehand, you can increase the recipe by 25% for results as thick than the original recipe intended. If you want brownies that are even a tad thicker than the original recipe, you can even increase the recipe by 33%."

The bottom line here is that you really cannot put the batter for an 8" brownie, cake, etc., into a 9" pan, as is. You should increase the ingredients, or find a recipe developed and tested for a 9" pan. ;o)