Unlimited uses.
I no longer have the book with me, but it's a magus with some merinita mysteries. In particularly he is making the inside of a bag much larger than the outside. The spell uses the Glamour mystery, but only to use Imaginem instead of the proper form of the bag (Glamour makes illusions "solid") - there's nothing in the Glamour mystery that suggests "space-warping" is one of its specific perks.