I want to script in a faction change and global event to mark the player as an enemy but I want this to happen ONLY during the day.

Is this possible you think?

I know the game somehow knows when a Vampire player is in the sun and then triggers their hidden SunDamager spell to hurt them. I'd like to find out where this is so I can add a faction change for the player vampire so that he is ONLY hunted and attacked during the day.

There isn't a script controlling the passing of time - that's handled by the game engine. You can query this information via http://www.creationkit.com/GetCurrentGameTime_-_Utility.

Cipscis

EDIT: Nevermind, I would just listen to Cipscis. I am still noob at all this.

Thank you sir!

This turned into a new problem. How does the game know to use the SunDamage spells on a Vampire player when the game time turns to day?

It isn't scripted into the vampire quest or the sundamage spell. Though the sundamage spell does have this script:

Scriptname VampireSunISMDEffectScript extends ActiveMagicEffect  imageSpaceModifier Property VampireSunlightISMD01  AutoimageSpaceModifier Property VampireSunlightISMD02  AutoimageSpaceModifier Property VampireSunlightISMD03  AutoimageSpaceModifier Property VampireSunlightISMD04  AutoMessage Property VampireSunMessage Autoint property VampirismLevel = 1 autoevent OnEffectStart(Actor akTarget, Actor akCaster)    if aktarget == game.getPlayer()        VampireSunMessage.Show()        VampireSunlightISMD04.applyCrossFade(2.0)        MagVampireSunlight.Play(Game.GetPlayer())        utility.wait(2.0)        imageSpaceModifier.removeCrossFade();        if VampirismLevel == 2;            VampireSunlightISMD04.applyCrossFade(2.0);        elseif VampirismLevel == 1;            VampireSunlightISMD03.applyCrossFade(2.0);        elseif VampirismLevel == 1;            VampireSunlightISMD02.applyCrossFade(2.0);        else    ;aka level 1;            VampireSunlightISMD01.applyCrossFade(2.0);        endif    endifendEvent;event OnEffectStop(Actor akTarget, Actor akCaster);    if aktarget == game.getPlayer();        imageSpaceModifier.removeCrossFade(2.0);    endif;endEventSound Property MagVampireSunlight  Auto  

Take a look at the conditions defined for whatever damage health type effect is used in that spell. You'll probably find that both the current game time, whether or not the actor is in an interior cell, and the current weather conditions are all checked using http://www.creationkit.com/Category:Condition_Functions.

Cipscis

Thank you again sir.

VampireSunDamage01 through 04