Hello,
Investiture is a very short exchange of prayers and would not take more than a few minutes, your priest should have no objections. Just print it out for him so he doesn’t have to look it up to save time.
Many believe that Investiture is “necessary” to "share in the “Sabbatine Privilege”. On the other hand an apologist on this very forum has stated that the Sabbatine Privilege is made only to those in the religious community that wear the Scapular as part of their religious habit, and not the laity. I am not in a position to say what the Church’s teachings are regarding this, but I am inclined to believe the Apologist as stated above.
The brown scapular is a sacramental, and it’s value is what it stands for in your faith and practice. I believe it is to remind you of your choice to show devotion. It is NOT a magic talisman. Investiture is just another step up the ladder of devotion, but it is your relationship to the Divine and your following of the Carmelite rules that are of prime importance, not wearing the brown wool scraps around your neck.
Just to be clear I wear the scapular and certainly do not discourage Investiture, I am only suggesting that your personal faith is more important than a few formal prayers over the scapular itself.
Regards,
William Unland