Air-layering cut-off time

BunjinEnt

Since you see the roots, It technically can be removed right now, however, it depends on the species and your knowledge of that species. a mild rooting stimulator might help it gain strength. If you have completely girdled it, it is running on its own anyway. Lop it off taking care not to damage any of the new roots. I personaly don't remove the moss the roots are growing in for fear of damaging them. Then plant in well draining soil/colander (see other articles on colanders/strainers) and protect from intense sunllight for the rest of the season. Read up on other articles on the care of the species in question. See also the
post-summer/autumn growth period. Typically you want to give about 2 months of autumn root growth before the night time temps reach below 60F.
Mid-Winter not a good idea.

Hope this helps,

-Wm