Do Cat Shines collected while Fury Bowser isn’t attacking deal damage?

In Bowser’s Fury, collecting a Cat Shine while Fury Bowser is attacking will lower his health for when you fight him later as giant Cat Mario.

If I collect a Cat Shine while Fury Bowser isn’t attacking, will it deal damage to him? Or are Cat Shines only effective if I wait for Bowser to start attacking first?