Enchanted Mirrors

Over the course of one minute you draw the spell's appropriate glyph on the surface of one mirror and then create its match in the negative space of the other mirror.  The mirrors float before you and remain floating nearby for the duration.  You then cast a target spell suspended between the two mirrors.  It strikes one surface and then reflects to the next, endlessly bouncing from one to the next.  The target spell can be any 3rd level spell or lower.  Only one spell can be suspended this way at a time.

For the duration, you can release the target spell as a bonus action, shattering the mirrors.  It does not count as casting a spell because the target spell was cast at an earlier time.   It cannot be countered because it was cast at an earlier time.  If the target spell requires concentration the caster assumes concentration when it is released.  If dispel magic is cast on the mirrors then the target spell releases immediately, either centered on the mirror or at a target at random.

At higher levels, you can choose spells of a level above 3rd for each level above 5th.