Put two 1x1 bricks a set distance apart, one named "timer" and the other "hit"
For timer:
onRelay -> Self -> spawnProjectile ["10 0 0"] [Radio Wave] ["5 0 0"] [1.000]
For the other:
onProjectileHit -> do whatever
When you fire a relay on timer, the events on the second will happen in a set time +/- 50%