[Newbie] Auto Blueberry first grow. Nutrients already in soil. When(if) to feed her ?

sinc you are in soil, wait until you see a hint of yellow on the cotyledons, then slowly start to ramp up your fertilization. If you use the same substrate of same proportions, you can pre-empt this timing next time. Take note of when it occurs and start feeding before that point next time. Trial and error.. so many moving parts that make your environment slightly different than another garden.