18h and sign of flowering

Yes it is normal for photoperiod plants to form primordia/pre flowers while there are still more than 12 hours of light, it does not mean they will start flowering, they are just expressingg themselves sexually. This can be likened to reaching puberty, but they are still a long way from adulthood (flowering). You have nothing to worry about and the fact you have never noticed them before means you have just not seen the primordia before, all photoperiod plants will show pre flowers/primordia long before flowering commences in my experience. Hope this helps, Organoman.