Hmm...
Well the whole city is underground and the light of the \"Blue Sun\" is nearly constant. Add to that that the energy emitted keeps its citizens from requiring sleep and you don\'t really have a day/night setting.
But I still like the idea though and each level/race could have different structure for each \"day\". Some could center on religion , others on work and the like.
Plus proximity to the crystal could affect the city in ways besides light, like buildings and items that were created closer to the crystal could be stronger and have various magical qualities related to the crystal?
What do you think?