if u want u can start them budding when ever u want. i wouldnt recomend starting them till they r bout 4weeks old, depending on space and strain u may want to start budding earlier so ur plants do not outgrow ur area.most strains roughly double in hight when flowering, so u may whish to take the distance from ur lights that they'll need 2b2prevent burning ur plants, if ur using hid bout 10inches is the closest they can b b4beggining to burn.floro's is bout 1-2inches.i have 2flower at different ages to take into account the stretch on the different strains. go to www.overgrow.com/strainguide to find a report on the strain u r using, this will tell you how much u can expect ur plants to stretch