Dominic Guarnaschelli’s new, site-specific installation is about the act of revealing something hidden. Perfectly timed during this season of massive gift giving, “Veils” features two parts: “Endless Time for End Times,” a looping video, and “The Gift,” a steel sculpture shaped like a gift box. Sheherazade’s 24/7 gallery is a gift in itself. To walk on Magnolia Avenue between Second and Third streets any time of day or night, and see art behind a large garage window — well, that invites conversations.