It's very hard, I know, and no one should expect perfection from themselves. It's "progress not perfection". I agree ... make a rule that you'll wait 24 hours before thinking of responding.
I had an abusive aunt who was a drug addict (ex-nurse). One day my brother came over and I took out the nasty, cutting birthday card she sent. He said, "so why are you hanging on to it?" Bingo ... that hit the mark. I had to cut all ties with her because what she said was harmful. (She was so abusive she was kicked out of a nursing home.) This was after years of hoping and wishing she would change.
All this is to say that it's a process.