Does Samadhi realm of desire require single-pointed focus?
There are no 3 realms of Samadhi(Jhana). The jhanas have nothing to do with sensual desire. First four jhanas lead to birth in fine material realms. The last four lead to immaterial realms. One-pointeness by definition is pointed at one object. At that moment all sensual desires are subdued. 

But it is possible to get in and out of the Jhanic  states quickly if you master them. ex: It is said that the Buddha enters the Jhanas between each word he speaks while maintaining a normal speaking speed.