Glaring Spotlight affects hexproof from all sources, regardless of their type or the timestamp order of their effects.
In many cases in Magic, when two continuous effects do opposite things, we must look at their "timestamps" to figure out the final result.
Glaring Spotlight, however, doesn't remove hexproof from anything; what it does do is change the rules for hexproof. This modification applies to all instances of hexproof on creatures your opponents control, including hexproof granted by enchantments and artifacts.
From the Oracle rulings for Glaring Spotlight: