As long as they're not in direct sunlight it shouldn't matter all that much. Direct sunlight may heat them to the point of changing the chemical composition. Also some flavors have TINY molecules that are released into the air inside the bottle so each time you open the bottle a little of the flavor escapes. Heat increases this effect - essentially making your flavors "lose flavor" over time. If you shake your flavors before use it can minimize this effect. Nicotine, on the other hand, oxidizes with light, so it's best kept in a dark cool place.

EDIT: Disclaimer - I'm not a scientist.... just a nerd.