when to lower N and raise the P

The plants won't require more P until they start going into flower. You will start to notice in mid to late summer the plants will begin stretching and growing more branches as the days get shorter. It's possible for them to almost double in size within a few weeks. At this point you'll be on the cusp of flowering and you can increase P and K, and start to reduce N. During the veg state, N helps the plants grow more leaves and give them that healthy green color, but it isn't as necessary during flowering. P & K will focus more on flower/bud development so you will end up with less leafy buds. Overall, your plants are looking great, though! Hope this helps. Cheers!