The G85 highway between Kunming and Song Ming is closed during the night (midnight till 8am) for a while, as long as temperatures stay below freezing.
This is done in order to prevent damage to the roads from frost by the large amount of trucks driving there.

I have no information how far the G85 and G60 may be closed or how many other highways are effected by this.

Please keep in mind the additional traffic jams due to breakdowns and peaks in waiting times at toll-booths during early morning and late evening.