I don't want to seem like I'm nit picking at you but even if it is your first grow and you are experimenting, why experiment for low yields. You are asking for help, so I will answer to help you get the best out of yourself and your plants. If I'm too harsh let me know and others will answer your questions and I'll bow out gracefully.
Here is a few things you need to learn.
First off patience.
Also only plant one seed per pot. To save money get sixteen ounce plastic dixie cups at the supermarket. They are around $3. Drill 5 3/16" holes in the bottom of one cup and fill half way with soil, maybe a little less. Give a good watering in the sink and let it drain for 20 minutes and then get another cup without holes and place the one with soil inside of it. Use what you want but I use an orange wire nut, I press it down in the soil and remove, then I place the seed in the hole and fill the hole with soil by running my finger over it. Then water directly over were you planted the seed ever so slightly, maybe 5 - 10 drops because you don't want to wash the soil out and cause the seed to be on top. Now place this under the lights you wish to use for Veg'ing. You should see sprouts in usually three days, of course you are using ProMix Organic soil and plain normal water, nothing else you will need. The only thing to watch for is sometimes the sprouts take off and grow quickly, then the stem isn't strong enough to hold the upper half, this is no problem for you because you planned ahead, just fill in the cup with soil around the plant as it gets bigger until the soil is almost at the top of the cup. No worries, mate.
While you are waiting, you should get a 2 - 3 gallon pot and a 5 gallon bucket for each plant you wish to grow. The reason is that you will be transplanting each plant right before Veg'ing and right before Flowering.
To transplant fill the bottom of the new pot with soil until the top of the old pot soil level is even with the new pots top. Read it a few times it will make sense. Take the plant, soil ball and all, removed from the old pot and place in the center of the new pot, then fill new soil around the new pot until it is all filled in. As an alternative you may just cut the bottom of the old pot off and then do the same above. I like to reuse what I can and afraid of destroying the roots when cutting off the bottom of the old pot, but experiment and decide for yourself.
Now back to your question, when to start flower. Whenever you want, that is what you decided but if you are trying to do it what I consider the correct way, I would not do it that way. If you are just trying to sex, I'd just cover up a branch. Back to the key word PATIENCE, I just wait for the plant to tell me what it is.
To get best results you should let the plant grow as long as you can, to meet my minimum standards I'd be waiting for 12 - 18 inches before switching. My newest method is to waqit for alternating nodes. If you have alternating nodes, then you'l know the plant is mature. Also mentioned on this board by another poster is to wait until you have 5 nodes on the plant which sounds about right and matches up with the other stuff, depends on how you wish to do it.
Hope this helps you out.