Virtual Reality enables users to explore content whose physics are only limited by our creativity. Such limitless environments provide us with many opportunities to explore innovative ways to support productivity and collaboration. We present Spacetime, a scene editing tool built from the ground up to explore the novel interaction techniques that empower single user interaction while maintaining fluid multi-user collaboration in immersive virtual environments. We achieve this by introducing three novel interaction concepts: the Container, a new interaction primitive that supports a rich set of manipulation and navigation techniques, Parallel Objects, which enables parallel manipulation of objects to resolve interaction conflicts and support design workflows, and Avatar Objects, which supports interaction among multiple users while maintaining an individual user's agency. Evaluated by professional Virtual Reality designers, Spacetime supports powerful individual interaction and fluid collaborative workflows.