It kinda has a timer.... if you look at the 5 different plant settings they control the light and I think the flow of water through each plant medium (spongy type foam). But the manual doesnt explain the amount of light for each choice. There are different seed kits that coorespond to each setting (sold seperatley). The machine came with the seed kit for salad greens. the seed kit contains the seeds in a foam cylinder and a hopper (type like holder) for the foam cylinder. It also comes with nutrient tablets specifically for the seed kit in my case the salad greens (ive been using them) was thinking about next time getting a cherry tomato seed kit and using those tablets. Ive heard marijuana is similar to tomato in some ways. You can see that i have mine set on tomatoes and peppers and this gives 16 hours of light and 8 of darkness. Some of the plants were started at different times because seeds werent readily available but the biggest gap in age is 2 weeks. The oldest are the 3 in the center at about 3 weeks....heres a pic of the settings... .
http://www.rollitup.org/marijuana-pi....php?n=450&w=o