They will get bigger the longer you veg them, then double or triple in size when you go to 12/12. I don't think I understand though. If you took your clones during flower, they need a couple weeks to revert back to the veg stage before they really start growing. I assume you know that switching to 12/12 is for when you want to start budding your plants. At that point they should have been vegged for at least a couple weeks, but more like 6 or 8 is better, depending on your space, etc.