every plant will act a little different because of the genetics or the age of the plant when you put it into flower. i usually veg. for about 6 weeks minimum so the plants are at least 18" or taller when i switch to 12/12. therefore i usually have preflowers on all of them and alternating nodes. so when i switch to 12/12, i seen nice buds starting to form after the first couple of weeks. i have went to 12/12 on other plants that i only vegged for about 4 weeks and it seems it took about 3 weeks before i saw any decent bud growth. so from my experience if you wait till you have preflowers and alternating nodes, you see a better bud growth earlier than if you do a short veg. time. the plants need to be mature enough before going to flower or it will take a little longer. but again the strain and genetics will influence this.