You can't tell a plant to suddenly mature at week # "xyz." I've grown a few different strains some were mature at 4 weeks, one took nearly 3 months. I've had males throw balls at 3 weeks from seed, and one didn't show mature until light cycle flipped to flower.
Anyways, this why people do clones, already mature, already grown and fairly predictable.
Breeders estimates are from a mature plant, and under the best conditions where these plants have acclimated, and adapted to, over several life cycles. This is why so many people get it wrong as they manipulate, flip when not mature, give too much light, over water, over feed, too cold, too hot, too humid, etc, etc, etc, trying to speed it up or force it grow "Big Fat Colas."
You're not really in control of it, especially when growing from seed.