Actually, the distance between Tomaru and the other platform is 15 feet, since he is on one edge, jumping to another.

[quote]Each platform is 30 feet in diameter and there is a 15 foot space between them.[/quote]

Tomaru jumps as Fuchsia is aiming at him, not as he fires a rocket. He doesn't need to be faster than the rocket, he needs to be faster than the time it takes for Fuchsia to aim plus the time it takes for the rocket to go the 25 feet you specified (and as I wrote in the post, he was already jumping by the time the rocket emerged from the hellzooka). Now, since this is a Tier 5 tournament where all the characters could "defeat Trinity from The Matrix with ease," I feel as though this is a reasonable degree of reflex and speed for a martial arts master. Furthermore, Tomaru doesn't even need to complete the full 15 ft leap before the rocket hits, he just needs to traverse a bit of it to avoid the initial blast and the rest is yet to come. 

Now, if the distance between Tomaru and the rocket, and consequently Fuchsia since he's holding the hellzooka, is 25 feet, as you are saying, we can use the Pythagorean Theorem to calculate the range of all possible altitudes for Fuchsia, which is 25 feet if he is directly above Tomaru, or 20 feet if he is directly above the edge of the opposite platform. Since he would likely be mid leap when he fires the rocket ~22 feet is a reasonable altitude. Even if we cut that number more than in half to 10 feet in the air, Tomaru is still less than 10 feet tall and could reasonably pass under Fuchsia given the near-linear trajectory I described.