In my opinion (no disrespect to anyone, I promise!), women who do NOT burn when applying the relaxer 1 day after washing are the rarity. I think the directions are for what happens to the majority of women.
Most people burn like the dickens and have scabs and weepy scalps and end up having to do more work to correct a bad relaxer than those who simply wait the recommended time. I relaxed the day after washing for the first time in my life just this past Feb 11th: I burned, I was under-processed (though I was okay with that), I created more work for myself, and I ended up having to correct some mild breakage issues as a result.
If your scalp is not sensitive, 2-3 days might be just fine.
I have a sensitive scalp, and 4 days with lots of tender preparation is always best for me. For me, 3 is too soon and by day 5, my scalp is no longer clean enough. For some reason, day 4 is the magic number for MY head.
I hope you find what works for you.
Blessings,
Christi