wildfire while shade is not the same as night if youve ever been outside at dusk or dawn you can clearly see that it does extend the dark period by a little such as a hillside or even in a small clearing in the woods if you still not convinced you might try it some time by taking a couple of clones from the same plant and place one outside where its not shaded from sunrise to sunset and place the other where there is shade only during sunrise and sunset and see wich one finishes flowering faster you can add an hour of darkness in the right location.
a plant 4 weeks into flowering is going to be concentrating on bud development and they will continue to develop for awhile after light cycle is changed much like when you switch to 12/12 they continue to veg and stretch for 2-3 weeks before it starts to concentrate on bud development.