Auto Crystal Widow

Depends what soil you are using. You want to start feeding a light mix soil after 2 weeks. A regular soil after 4 weeks and a heavy soil after 6 weeks. Usually your plants got enough nutrients inside the soil till the leaves are as wide as the pot. So when the leaves cover the size of the pot you can start feeding. Always start with a low amount. 1/3rd next time 2/3rd and then the amount that you want to give. Plants do not like heavy swings with nutrients.

Definitely yes, when it's autoflower, start with half amount of nutes.