Nearly 4 months after FUE, do the follicles sprout at different stages? Will new hairs sprout after 4, 5 or even 6 months?

At four months it's really kind of a frustrating part after the procedure. You've invested a lot of time and effort and money into getting 3500 grafts and it's frustrating, to think that it's delayed satisfaction after getting the procedure. Especially at three months to four months, most of the hairs that were transplanted are still dormant but generally at four months and as you get into the six month range, there should be a lot of activity for growth. 
If the procedure's done correctly, I'm talking all the grafts are cored correctly without a lot of damage to the grafts, either coring or pulling the grafts, and scoring the grafts done adequately and also placed adequately, generally as is with my patients, I see 60% to sometimes 80% full growth at six months. And this can vary from clinic to clinic. Sometimes it takes longer but I think in the next couple of months, you gonna be quite satisfied as new hairs are growing in and start to thicken. Also, it may take a total of 12 to 18 months after this procedure when you have your final results where the hairs have thickened to their terminal growth, which is your end growth stage and have also come back as far as luster and overall texture to a normal state. So, good luck.

Usually we can see nice result after 5-7 months but for full regrow you should wait 10-12 months. For crown part even a bit longer.