No it isn’t too late. Knock-out roses fall into the category of landscape roses. Here is information on pruning them-
“Pruning landscape roses is very simple. Like other roses, they should be cut back before winter to around 30 inches high to reduce their loosening from the ground by winter winds. Then cut them back a little more in the spring. Start by first removing all broken or dead canes. To maintain size, cut them to about 20 inches. Soon afterwards they will sprout vigorous new canes that will produce many blossoms. Periodic light trimming of the canes may be needed to keep them within bounds throughout the summer. These roses are self-cleaning, meaning that after they bloom the old flowers drop off cleanly with no hips remaining, so routine cleaning is not needed like with other roses.”
The complete article is here, should you need it-
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