Why can't I use the Slow Motion feature?

The slow motion functionality (tap & hold in playback) is only available in the 120 FPS preset at the moment.

120 FPS recording is only supported by iPhone 5S devices.

60 FPS recording is supported in iPad Mini, iPad Air, iPad Mini Retina, iPhone 5, iPhone 5C and iPhone 5S, and offers natural motion recording but not slow motion capabilities.