Traditionally, it's considered that flavor additions go best at 15-20 minutes and aroma additions at 5 or less. Then there's dry hopping which adds aroma, and flavor because aroma=flavor.
BUT as flars and sneezles suggest, everyone's palate and preferences are a bit different, so do some experiments over your next few batches and see what floats your boat.
By the way, the Brulosophy XBments that sneezles references are very interesting. I think I'll be doing some experiments of my own soon.