If there is 20 to 25 chicks to a box, they will be fine. If less, they might need some hand warmers on the sides of box to keep warm during shipping. You can ship them at almost all times and they will be fine. Adviseable NOT to ship when there is temps under 10-20 degrees outside. 15 chicks they can handle 30 degrees in shipping without too much problems. If you dont know for sure, order all males packing peanuts to help the pullets thru.
In most cases, they will be fine! I would have done the same if I need some layers in the spring so I order chicks now until Dec to get them going.
Go for it!