How tall are your plants now? You're going to flower in 18 days? With your plants as small as they are? Your plants look healthy, but I don't think they are any where near maturity yet. Oh well, do what you wish I hope it turns out well for you.
You can flower those whenever you want, they look good and healthy. It really just depends you much yield you're looking for. Generally speaking, more veg = more bud.
I've read many posts on this site where people have gone to flower much sooner than you, some even almost as soon as the seeds pop.