There's a straight forward procedure. Declare, put the mask on, wear headset, check interphone receiver on and volume adjusted, hot Mic on and check with the PM. Execute the first step. The hot Mic may be put off if breathing sound becomes too loud. Ask for ECAM actions. According to Airbus Second step is done with ECAM. Some airlines have a little variations.
Descending at VMO/MMO with speed brake half full it takes 4mts and covers 40miles to reach 10000ft. from 39000ft. If at less speed due to damage then may be 8 to 10mts.