I agree with Foxy, I generally don't experience problems when I switch from flowering to continuous light for a week or two. Also, many of the times that I've done this, I was transplanting and added a good bit of rooting hormone to the new soil. Sometimes I didn't even need the continuous light, but was able to switch back to 18/6 immediately and got new (and vigorous) growth after one week or less.

By the way, is SuperThrive still on the market? I remember being able to find it at Home Depot at one time, but can't seem to find it at any of the major retail chains anymore.