i can root cuttings in 10-12 days with a regular propagator, they will then need about 4 weeks veg maybe 5 to produce a 1lb plant,
i don't think i could do it with only 3 weeks veg from clone, perhaps with some crazy haze cross
from seed, i can get the seeds under the light in 3 days from starting to germinate
21 days later they are 8 inch to 1ft tall , i would not describe seedlings as spindly as you describe your seedlings
if flowered now the right genetics can produce 1lb from seed from an 8 inch to 1ft seedling, i have done this a few times with seeds
with clones they need 5 weeks with all the genetics i have grown, perhaps some crazy haze strain could get this big with less veg time
but will most likely need more flower time
peace