Interiors are from the first quarter of nineteenth century.
The quotation from a museum's website:
"The White Room showcases a perfect harmony and symmetry of all elements. It is positioned in the center of the second-floor enfilade, and demonstrates unique interiors of St. Petersburg's palace of the first quarter of nineteenth century. In spite of some detrimental changes caused by remodeling of palace during its conversion to a museum, this room still enjoys original paintings and sculptural decor, as well as period furniture designed by Carlo Rossi himself. Many masterpieces of decorative arts are also here. Very remarkably, the artistic excellence of White Room was so highly praised by the contemporaries, that the model of the White Room (1/8 scale) was given as a present to King George IV of England."