The hips have to open before the shoulders. If you look at the best pitchers, in many cases their hips leads their shoulders by up to 90 degrees.
This has nothing to do with rushing.
When you are occasionally rushing (e.g. sometimes missing high -- especially when trying to throw hard), then your timing is different so that sometimes your foot plants sooner than others. If you are habitually rushing (e.g. always missing high), then you need to so something like break your hands sooner so that your arm is up and ready at the moment that your shoulders start to rotate.