Four albums in, NYC disco brats Scissor Sisters have settled into a groove. It’s a good groove, no doubt, but it’s a groove nonetheless, and one that keeps them spinning in a single direction that’s starting to feel like a musical prison. Once again mixing Eurodisco, electro-pop, glam rock, and ’70s radio pop, Jake Shears leads his crew through a set of songs mostly about having a good time. Magic Hour is all about living for the moment, a perpetual Saturday night where the dancing never stops. The best songs here stand out because of their collaborators: Buzzing Scottish producer Calvin Harris injects “Only the Horses” with a slinky R&B beat that gives way to a pulsing club chorus, and red-hot Harlem rapper Azealia Banks smacks some street into the hip-hop-leaning “Shady Love.” But the rest of it is a dance-floor blur.