it all depends on the strain, what you are trying to yield, what lighting, are you using co2, basically alot of variables. If you want more weight obviously vegging logger is going to help. A seed is going to take around 2-4 weeks to reach size of a clone (again depends on a number of variables). Generally, disregarding lighting or anything else, I find the larger the area the seed has to grow into will also determine how big and fast it grows.