Their recommendations are about right, if your pump runs 24/7. Otherwise, not so much.

The only reason to clean the pump / skimmer basket is to keep you from dumping stabilizer out when you clean them. If you clean the pump and skimmer basket first, on most pools they won't need cleaning again till after the CYA is fully dissolved.

On a 26k gal pool, 5# of CYA fully dissolved will give you 23 ppm of CYA, so a measured level of 15 ppm is well within the range of error.