30 seconds is long enough.
You can press need on items if people dash around and open chests while in combat, I do this all the time while tanking big groups and it doesn't interrupt my rotation at all (the GCD is 2,5 seconds, more then enough to press need on items and for multiple items you can press need in between you press your keybinds in your rotation).
Cutscenes are no excuse, MSQ roulette has no loot and SE can change so that scenes play when you exit the roulette.
This doesn't work for me, I have on many occasions had DC's when the final boss died, I log back in in less then 15 seconds and there is no loot window or anything, whenever I DC I loose my right to loot. This was a real issue for me in the past but now I use a VPN so I don't DC anymore.