Good question, and welcome to RIU. If the grow space has an even carpet of green, both methods will yield the same amount since you are fully utlizing the light, and assuming you feed the plants properly. The one that will take less time is the one that involves the smaller plant since it takes longer for the plants to grow bigger. There are some that will immediately switch to 12/12 once a clone takes root and will get a small amount off bud per plant, but with the increased number of plants they end up pulling in a decent crop. Seedlings dont work that well since the plant itself isn't mature- clones work best for this.