Drat, dead-heading flowers will beget them to rebloom..as soon as flowers start fading, remove..
Your butterfly bush should bloom until Aug/Sept..Hardy Hibiscus are late bloomers, but should remain until Sept..depending on your climate. W/good care, hibs bloom continuously..Toni

I cut back many plants simply to keep them looking somewhat tidy. Actually, most do NOT re-bloom for me. However, Salvia, Speedwell, Veronica, some daisies, some sedums...do.
And, all minty-type flowers like monarda, sage, catmint.
Some geraniums also have rebloomed after a clip to half height. And some delphiniums will send out smaller side shoots that bloom after the main big bloom is cut. (much like a broccoli) Cut back and take notes as to what comes back for you. Lucky you to have a ready-made garden.
Pondy