Having a fixed flight time and having a different launch angle isn't physically accurate since it requires each cannonball to have a different gravity.
Do do a launch here are the formulas. "angle" is the launch angle and t is the flight time. You'll need to change event 5 to use ball.gravity instead of gravity in the equations.
ball set vx to (x_target-x_start) /t
ball set vy to ball.vx*tan(angle)
ball set gravity to 2*(y_target-y_start-ball.vy*t)/t^2
Probably no, the turret behavior is for straight shots, but with some creativity you possibly could do something similar with events.