How fast does Fireball travel?

Fireball says:

You point your finger and determine the range (distance and height) at which the fireball is to burst. A glowing, pea-sized bead streaks from the pointing digit and, unless it impacts upon a material body or solid barrier prior to attaining the prescribed range, blossoms into the fireball at that point.

Does the bead hit the target instantly or does it have a travel speed?

I’m wondering for the application of hitting a moving target at a distant and need to know if I should lead my target or aim directly at it.