From that video it appears the unfolding sequence is set to occur prior to the insertion burn into L2.

If the JWST will in fact spend almost a month in earth's orbit, does someone have an educated estimate on the magnitude of risk posed by space junk to nominal deployment?

Looking at those solar shields I imagine that they could be destroyed entirely by even the smallest of debris fragments. Same with the mirrors.

Edit: I'm wrong here (thanks @thethirdone). The burn set to occur after deployment is the L2 insertion burn and not the transfer insertion burn. Most of deployment will occur in the transfer orbit en route to L2, far away from earth-orbiting debris.