The body part ownership is elicited in 23 s, and the full-body illusion is produced in 5 s. Our previous study has shown that synchronized hands and feet movements produce the full-body illusion at an empty space between the hands and feet in 5 min at most, but the exact onset time is still unclear. This study investigated the optimal learning method and learning time for the invisible body illusion by measuring the onset time of the illusion in active movement and static observation. As a result, the illusion was produced after 6.93 s of synchronized movement or 4.67 s of static observation. These results suggest that both active movement and static observation are effective for the invisible body illusion.