I've done it the same day as a Phyto relaxer (Index 1) last month.
But I was being daring: I took down a sew-in, clarified, 2-stepped, IN THE SAME DAY and my scalp was like: GIFSoup
Never again. And Phyto relaxers are VERY mild.
You should be fine with using a protein 3 days before relaxing. I would recommend a light protein as a midstep (after rinsing out the relaxer but before neutralizing) as well.
I've done it three days before. There were no problems, just make sure that you don't scrub at your scalp too much during the treatment and that your scalp is based well for the relaxer.