This is Slow Glass as predicted by British Writer Bob Shaw. Half of your windows could be 12 hour slow glass, so sun is always shining outside.
Note that this is not an actual material. They stored the light in a small group of ultracold Rubidium atoms floating in a vacuum chamber, and keep in place using lasers. And they moved the group of atom 1.2mm (.04in).
(They also probably stored the information of a single photon.)