the oldschool method before the pbaoe team bubble change was 4 minutes for each shield applied. Made it quite weird buffing cycle of Powerboost + 4x shields on teamates, then 2 minutes wait for power boost to come back up to buff the remaining 4 players.
When I came back I was in shock after finding out it went from single shield to the team targeted aoe it is now. Super QoL addition, not sure who did that but that was 70% the bubbler's work at least in those days.
Way back there was a program called herostats anyone could remember - that kept a timer on screen for various buffs, kinda like what overwolf does now for some games.