I also use Xpert Nutrients. My autos do be big with these Nutrients. But autos flip whenever they feel. But typically the times are between 25-35 days of veg. Sometimes I get autos that flip into late week 3, or a major thing that flips them is stress or shock. Lot of the time. Its tranplanting that shocks them. In this case it's light shock + exhaustion.
If you look up DLI you'll learn a lot about what I'm talking about.
Good growing pal