In projectile motion, the total flight time is ______.

In ideal projectile motion over a level horizontal surface, the path is symmetrical. The time taken to reach the maximum height ($t\text{up}$) is exactly equal to the time taken to descend back to the ground ($t\text{down}$). Therefore, the total time of flight (T) is twice the time required to reach the maximum height:
$$T=2\cdot t\text{up}$$