Burnt plants a bit with nutes for growing. When to start giving them nutes for blooming? (autoflowers)

in the second picture they look very green, which usually indicates too much nitrogen (and the burnt tips would also state overfeeding).. In regards to blooming nutrients, i would wait until they finished the stretching phase at the beginning of bloom.. during this time they will still require a lot of nitrogen for growth, which is usually not that much available in bloom-nutrients. the switch to bloom should be done when the stretch has finished and the plant focuses on fattening the buds.. starting at "600 ppm" would mean an EC of 1.2, which for soil would be too high.. for hydro or coco this would be fine, but without knowing what medium you grow, that's difficult to judge.. i suggest looking at this link to look at how (much) to fertilize: https://www.mandalaseeds.com/Guides/Fertilizing-Smart-Guide