How would you adapt the portion size and baking time to using smaller, individual sized (6") spring-form pans? Thank you!

A 6 inch pan holds about half the volume of the 8 inch pan specified for whole recipe.
Whole recipe serves about 8.
So the 6 inch pan will serve about 4 people with half the recipe.

For individual servings maybe use 4" cocottes. Estimated time will be about the same for baking creme caramel, so look at a recipe for that.