1. u need to revegg your plants if your going to flower then again, not worth it just start over.

2. You can change your light period, it will shock the plants, i would suggest leaving them on until you want them to go off and then start the schedual. Either way u can do it with out a large off or on time difference. Plants dont get too shocked from this, but it will take a day or 2 for them to realize what has happened, your might be better off leaving them alone, let some one else give u another answer to this.

3. u can vegg for however long you want, just switch the hps in and set it 12/12 and they flower, i would give at least a month of veggin

4. Depending on your temps, put the back side of your hand at canopy level and raise or lower the light depending on the strength of heat on your hand, u want it to be warm not hottotot