I’ve had a few at 7+ weeks before flowering. Most have fallen in the 3-5 week range.

Cannabis plants can reach sexual maturity at 4-5 weeks old. Doesn’t mean you’ll ever see flowers in a month. The transition to flower time is 100% dependent on the photoperiod/s it was crossed with. After a plant has reached sexual maturity it will still take several weeks to begin showing early bud sets.

Is there any media under those rocks or is it 100% hydro? If so, what’s the water temperature? About 68-70F is where you want the water temperature with hydro.