One of the keys to reaction time is knowing what you are going to do in advance. So, by yourself, you can kind of program your mind.(and keep in mind that you never practice avoiding a punch without practicing the counter)
So you envision a jab coming to you and catch it and jab back in the same motion, small pivot to your left as you do so. Then you parry it over your left shoulder with your right hand, and bring your left hand up...The list goes on and on.
You teach your mind to react, teach your body. When you get into the ring at least that basis is there.