The only thing that SOME Elphaba standby's do before a show is maybe put on foundation. They never actually get into the green until the word is given.
I've heard some of the makeup artists have done the full transformation in like 7 minutes. I think it recently happened on the 1NT when Emmy Raver-Lampman took over mid-act two for Emma Hunton. The makeup artist on that tour was able to get it done in 8 minutes or so.
I think the whole they MIGHT be able to leave after "No Good Deed" but that might be false.
"Life in theater is give and take...but you need to be ready to give more then you take..."