I would say anywhere from a week and over because the last two times I did my relaxer the new growth started peaking in after the first week. Although, I USUALLY notice it at around 4 weeks so that's what I picked.
I had to go with about a month. Which was weird because I was getting NG but my hair was always NL Ah well. I haven't had a relaxer since about mid to end of January and have a good amount of NG...I plan on having a relaxer...maybe lol...in December for the holidays and New Years to start my year off with a BANG So we'll see lol