With something like Round Up I would think it fine to go ahead and plant bulbs, but Ground Clear indicates it prevents growth for an extended time unlike RU. For it to do that I think it would have to seep into the soil. Daffs are tough, and planted deeply they would probably be okay. Might see some mutations among them though, like variegated leaves.
If the bulbs were already present but dormant at the time of spraying, fall rooting time would be the first exposure they've had. Enough of the toxin may have filtered out of the soil by the time they started rooting.
