Vegging can be done to the exact moments you get roots on your clones to veging until you have a 7 ft high tree. it all depends on the pot size you use usualy its 1 gal per 1 feet of growth. so it depends how much room you have for upward growth flowering dobles to triples the plants size usualy indicas doble and sativas triple. take into account space you need to keep your light from the tops. flowering sativas can be as long as 14 weeks and flowering indicas usualy go for about 8-10 weeks. when judging your stuff to be ready you get a microscope and go by the tricomes when they are 50% clear and 50% cloudy you get a uplifting non couchlock high but if you let it go longer for instance 50% cloudy and 50% amber you get a couchlock high. when judging when to cut down. i would wait until you think they are ready and then wait a week more. Good luck
Seedling stage takes about -2 weeks...veg for me can take anywhere from 3-6 weeks depending on my space, pot size, and how big a plant or plants I want. So a total of 8 weeks max before I flip my lights to 12/12...then if it's an indica it typically goes for 8-10 weeks, sativas 10-13 weeks in flower. I check my trichomes with a mini microscope, when they are all cloudy and some amber and my stigmas or hairs are 80-90% red I cut her down, good luck.
aerogardens are quite small and work well for starting clones. while a full grow in one might be a fun project, there is not much room or power (light output) for particularly useful flower yields. But again it would be fun, and you'll get to learn how the plant grows and develops precious, tiny buds. I'd suggest flowering with 12/12 schedule directly from seedling to have any shot at keeping growth confined to a stock aerogarden. better still, i'd suggest a modding the aerogarden for more space or going with more adaptable, robust lighting equipment, and then using a vegetation period appropriate for whatever size the growspace is. if you stick with aerogarden, investing in a very short autoflowering variety might be a better match than unknown seed. cheers, and have fun!