you want to let them root (develop a root system). what do you have them in now that you need to transplant them to cups? rockwool? if you want you can veg them under 24 hours of light. a lot of people do. it speeds up the veg process. if you are in rockwool wait till you see roots coming out of the bottom. make sure the soil you transplant them to does not have a ton of nutes in it and don't feed them nutes till they have 3-4 fully developed "true" leaves. you can feed them a seedling solution or just tap water that you let sit out for a day to evaporate the chlorine.
Cool. Thank you
How long should they stay in cups for till I put them into five gallon pots?
Also should I stay 24 hrs in cups or go to 18?
I am using rock wool
Does anyone else concur with the going right into five gallon pots technique?
As for container size, the bigger the better. A larger pot holds more water and nutrients for a longer period and you don't stress the plants by transplanting. For me though, it's more of a space issue. My indoor space is 2'x2' which means I can either fit one five gallon container, four one gallon containers, or a single 72-cell nursery flat. I choose to do the four one gallon containers. It provides a reasonable amount of space and I don't have to worry about watering 2-3 times a day, since I like to keep them indoors for two to three weeks before taking them outside to finish. When choosing your container size you want to weight all your options and make a decision based on how you grow and what your comfortable with.
I would assume it depends on how well your potting mix is able to drain. When I've used large containers, it was with terra cotta clay pots using a peat moss and perlite mix. Gravity would force most of the water towards the bottom and the pot itself sucked in some of the water and created a sort of vacuum affect, forcing air from the top to the root zone. So I didn't see any stunting in my grow, but I believe you have a valid point.