Switching to flowering in a hot soil mix

Hey guys. The dude at the hydro store really wanted me to buy a bag of Just Right Xtra, looks like some good stuff. The problem is it comes pre-loaded with GH products and I've got no idea what the NPK value is. I'm going to be vegging clones in this stuff for only a week or two then I have to start flowering. Is a simple flush enough to make the transition from veg to flowering?

Perhaps I was not clear. Clones will only be in this soil for a week. Not enough time for it to eat up the nutrients that are pre-loaded into the soil mix. Will I burn my plant if I start feeding micro and bloom nutes after a week when I switch to 12/12?