^Exactly.
When the plants receive complete darkness, an auxin starts to build, when the night is longer(12hrs), this auxin builds to where it passes the threshold for the plants genetics to flower. So, if you were to interupt them in their complete darkness with a light on them even for 1hr during the night like mentioned above, emedietly these auxins are broken down back into the plant and it never reaches that flowering threshold that is encoded in the genetics to flower with long nights.