Using established data of time of useful consciousness before hypoxia sets in for passengers unaware of the time to rip off their masks and don oxygen masks; 9-15 seconds@45k feet, 30-60 seconds@35k feet, 2.5-3 mins@28k feet. I presume a new normal of flight attendants adding "Rip off your mask immediately when the oxygen masks drop down from the overhead bin and… blah blah blah. I don’t know of new placards will be printed for passengers on commercial flights.