Depends on strain. Most 8 week strains will show flowers in 2nd week as a good rule. I have had some come out in the 3rd week as well. I grow Sensi's Northern Lights and that is a 7 week strain that I see flowers showing at the end of the first week to the first few days of the second (usually withink 10 days). I have done a thai that didn't show for almost 5 weeks. (it flowered for 19 weeks though). For me, I find most strains show flowers starting from week 2 - end of week 3...