This is the very beginning of flowering, but don't be too eager to switch to bloom nutrients just yet, your plant still needs adequate nitrogen during early flower.
I prefer to stay with grow nutrients until there are small budlets/tufts have formed, before switching to a half/half mix of grow and bloom for the following 2-3 weeks and then switching to straight bloom nutrients through until maturity. This seems to produce the biggest flowers and on plants that don't exhaust themselves and end up a sickly yellow colour by harvest time.
I have been using this method for 25+ years and swear by its effectiveness.
Hope this helps, Organoman.