How do you know when your plants are flowering to change the light from 24/7 to 12/12? Do I just wait for buds to appear Or do I just change the lights to trigger the plant to flower after a few months?
The plants won't flower until the light schedule is changed. From there it usually takes about a week before they're actually flowering. When you flower is up to you, but keep in mind that they'll grow 2-3x their size in flower. This doesn't apply to autoflowering plants as they will flower based on age, generally around week three.
It's entirely up to you - there's many factors involved... Like I said, keep in mind they'll get 2-3x their size in flower so make sure you have enough space. How much light you have is also important as having a larger plant isn't going to yield more if you don't have the light to support it. It's specific to your setup/preference.
I think MJs are ready to flower when their nodes are alternating.. At first you'll see that each node have 2 set of leaves, but after a while, your plant will start to grow alternating nodes with 1 leaf each node. This is the time when the plant is ready to flower and start changing your light sched to 12/12, 11/13, etc., depending on your strain. Usually sativa dominant strains takes longer to mature and flower like what im experiencing now. But I saw others growing 12/12 from seed. I don't know what are the effects of this in some strains.
Not always true. Some strains will start flowering even under veg lighting, if they are ready. To the OP, flowering begins when...you see the first signs of flowers developing. Many make the mistake of counting the "flowering" period from when they flip the lights, only to find that the strain took 1-3 weeks longer to harvest than the literature suggested. That because they started counting too soon. Remember that "flowering" is a plant life stage not a timer setting.