In my department, first due truck (our Engine 3 for fires) the crew all dons SBCA enroute while seated, the ones that aren't juniors. Most don't don facepiece until they reach the door. As for me, atleast during trainig, I try to put it on at the last minute, to avoid it fogging up and becoming uncomfortable. Not that my thoughts count, I'm just a Jr! Hah.
we pack enroute and mask when we need it but if i know we are on the way to a working fire I might put the mask on but I am just the backseater so it really doesn't matter for me to have it on i can see just fine to grab the hose and head to the door the officer on the other hand i dont think should have the mask on till he is about to enter.