Mine take only a few days to attach to rubble, then up to about 2-3 weeks before they are a full circle (from a half slice and a smaller shroom). With the substrate your using, why not use Rubble or Shell. I place all cut shrooms in a tub (in tank) filled with crushed coral. The shrooms attach to the smaller crushed shell, and I then glue the smaler shell onto a piece of LR. This saves the Shroom moving from its glue.