I agree with this completely. From what I have done with par t5. Too much 420 nm blue during flower slows flowering. Too much 630nm and/or 660nm red during veg will slow down growth.
In flower with too much blue, it does make them take longer to finish. But buds are smaller. So you do.want more red than blue during flower.
Look what I posted in another thread.
LED Without LEDs -My First T5 Grow