16/4? Where do you live? Where I live we have 24 hours in a day. You can switch to 12/12 whenever you want. Just keep in mind that the longer you veg (24/0 or 18/6) the greater your overall yield will be. If you want a sign from your plant as to when to switch to 12/12, look for alternating nodes. Good luck.
If you plan on vegging your plants, get them on a schedule when they break the soil. I used 18/6 for my vegging plants, but a lot of people do 24/0. You could also put them on 12/12 whenever you want. Some people start 12/12 from seed to keep the plants a bit smaller.