How can I use the creation kit the edit the amulets of night power? For example, changing the duration of the summoned gargoyle or increasing the damage of the bats. Or is this in a script?

I believe all that you would need to do is go into the CK and edit each individual amulet's enchantment's magnitude/duration.

https://skyrimmoddingtutorial.wordpress.com/2012/03/30/applying-enchantments-to-an-item/

They actually don't have enchantments, and their effects are not considered enchantments. Probably explains why you can enchant them in game.

There's probably a script associated with the item then.

How would I find that script?

Not at my CK, but...

The script is probably under Data/Scripts/Source/Dawnguard.

Move it and the other (psc?) dawnguard scripts into the main Source Folder, and you should be able to edit them in the CK like you can other scripts; from there, you could check the 'UseInfo' on the amulets to see which Quests use them, and then edit the attached Scripts.

Edit

Right, at the CK...

The Summon Gargoyle looks like it has it's own Spell: DLC1ConjureGargoyleLeftHand -- that has a duration of 60; so you should be able to just alter that directly. Bats likewise has spells such as 'DLC1BatsDmg".

So I assume you could alter them without actually doing anything with a Script?

There isn't a Dawnguard folder in there, but I see the script in here: http://gyazo.com/f12e0ddc8e039257b849f8f1abfa5027
How can I edit that script?

That's weird...

Well, you could try extracting the Dawnguard.bsa file, that should contain all the Scripts; without the actual .psc script, you're not going to be able to edit it; I'm assuming it doesn't let you edit the Source when you right-click on it?

For what it's worth, it looks like that script uses a .wait(30) command to make it's effects last for 30 seconds; so once you can open it, you should be able to just change that to any other number to alter how long it lasts.

I used a bsa unpacker but I don't see that script in there... is there any other way to edit it?