Illumination: Tree Lights at The Morton ... - The Morton Arboretum During Illumination, the East side of the Arboretum will close at 3:00 p.m. to prepare for Illumination opening each evening at 4:30 p.m. Rentals must be returned by 3:00 p.m. However, those with their own snowshoes or skis may enjoy the many trails on the West side of the Arboretum until sunset.