Barberry and Euonymus you could cut back any time since you are not growing them for the flowers. The Mock Orange (if by that you are referring to Philadelphus) should be cut back after flowering or you'll lose the bloom for this year.

depends how big.. and how you mean to cut back ...

if the MO is huge.. there would be no reason to do some proper rejuvenation pruning ... youll only lose the flowers you cut off with the large branches ...

if you mean.. giving it a hair cut.. what flora said ...

ken

Ok, thank you to both of you. I will trim back my burning bush and also my barberry (it's much bigger than the barberry beside it and I'd like them abit more uniformed) and I will leave the mock orange until after its finished blooming.