Real time saveing refers to save states. A save state is basically a complete snapshot of everything that is going on in the system at that point. If you can save this information and restore it later, you can save and load a game at any point during gameplay regardless of whether on not the game would normally allow that.
Currently, no flashcart can do this with DS games. The CycloDS Evolution claims it as one of its features, but it is not supported on the current firmware.