New problems i

so i was just refining my grow box for better growth and better lighting and my bigget plant had a light fall on it and chop off the top half. :/ so what might this do?? i have 4 plants in like a 1.5X1.5X4 ft box and i have had them growing under cfls from seed for like 8 weeks so i want to start flowering today is this all sounding good and question and comments would be much apprecieated the plants are each about 9 inches tall with solid green leaves and consistant growth.

thanks for hlp how many days into flowering till the preflowers start showing