Many growers opt to start @ 12/12 in comparison to an AutoFlowering strain.
I would start @ 24 hours per day during the seedling stage through till you see serrated edges on your leaves. Once you see that growth you can change to 12/12.
I you have not already picked up the following, I suggest that you do and incorporate them into your setup.
Figure 8 Cord (You will need this in order to plug your hood into the wall outlet (or extension cord); replacing the use of the Figure 8 cord built into the base of the Aerogarden. Also for use when raising the hood beyond the devices built in limit)
Air Pump, Air Line and Air Stone. (About $20 CAN total; can be picked up at a local pet store. )
Additional lighting. Being you have opted for an AeroGarden I take it there is a reason. That said, I expect you'd be using CFL's rather then a HPS add on. Be sure to pick up the correct CFL bulbs for Flowering and not vegetative growth. (Considering your potential course of action)
The AeroGarden Rocks for what it does. (Albeit, if I had the knowledge and means to build by own DWC; I would....)
Don't bother messing with the PH values in the water, pick up 1 gallon containers of distilled water.
if your Veg/bloom nutes are liquid, I suggest the following.
Plain distilled water (From germinated seed -> use of one full gallon of distilled water)
1/4 tsp of nute (Prepared gallon of distilled water w/ 1/4 tsp (Smaller of the two spoons) Nutes mixed in well *Just shake the shit out of it when you add the nutes*
use that 1 gallon of Prepared distilled water to top off 1 week into grow. Top off daily after which until prepared 1 gallon is totally used up.
3/4 TSP of Nute per next gallon
1 full per additional gallons
Make sure you cover the other holes in the Aerogarden
don't use a mirror as reflection
don't use tin foil anywhere
let it grow and leave it alone
Finally, the best AeroGarden advise I can provide is Preparing the sponges for the germinated seed.
(Germination)
hint (Use distilled water)
do NOT allow the tap root to get any longer then 1CM before you place it in the sponge.
Prepping the sponge.
Take a ChopStick and burrough a hole down the centre. twist the chopstick so it drills down to the bottom of the sponge and pops out. Spend some time on this ensuring that you don't ruin the sponge and that you prepare the sponge for the root growth.
Basically you open up a pathway for the root to grow down towards the water in the reservoir. I feel it speeds up the growth and encourages/increases the success of the seedling when it roots easier. :>
Finally, you will not run out of room within your res unless you have a small 3 pod AG. if you have a VeggieDelux, (for example) you are more then fine. :>
Hope that helped!