I think in general cuttings are best taken in the spring when the plant is strongest, however I have had success with cuttings taken in late summer also. If you wish to transplant in the fall then they shoud be from spring cuttings where as late summer cuttings should be held over winter and planted the following spring.

I have had most success with softwood cuttings and new shoots. I did pull a Mock Orange sucker late April (with a portion of the roots intact) this year from my mothers land and stuck it straight into the ground at my house. It has since been leafing profusely and looks to be in good shape.

I think the general concensus (from my own personal probing) is softwood cuttings about 5" long in the spring in a 50/50 mix of moist (not soggy) peat and perlite as a medium. Cover with a bag to hold moisture in, leave only a few leaves to prevent moisture from escaping via transpiration. Allow fresh air to circulate every few days.

Good Luck!