Delayed Spell says:
...Only spells that target one or more squares or grid intersections can be affected by Delayed Spell...
Fireball mentions its target as:
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.
Would that count as targeting one or more squares or grid intersections?