Attacus atlas hibernation

In a week or three I have some 40 cocoons of attacus atlas butterflies. I raised them on ligustrum ovalifolium but that is pretty hard to come by in winter. So I would like to hibernate the cocoons over winter so they would come out around the end of may.

Now I already looked up some information and it said that you can only hibernate them on diapause for some 4 months tops on at least 14°C. Then they would hatch in the beginning of April and Ligustrum is not sprouted at that time.

Someone here with more experience how to solve this?