When should I add spices?

I'm getting ready to start a holiday ale I came across that includes nutmeg and ginger. I've never fine anything with spices before and i'm trying to figure out when the best time to add them is, whether during the boil itself or in the secondary. Which is going to give me the best flavor and presence?

I just brewed a Spiced Porter from Austin Homebrew and the recipe that came with the kit had the spice add at 15 minutes left in the boil. The wort had a nice spicy flavor, but not overly so.

I don't have a ton of experience but my feeling is that if you add earlier in the boil, you will lose flavor and if you add when putting it in the secondary (or adding to the primary after initial fermentation), then it will be too strong.

Spices are mostly for aroma, so towards the end of the boil, as the above poster said 10-15 mins before flame out.