Something like a crossed swords icon next to the rest of the icons on the top left. Red swords - raid time; green swords - raid is over. Well, and a function to disable the icon for those who don’t care/need it.
It’s just different time zones, wrong time on the computer clock, or server restart latency and all that… It isn’t very clear. A raid time icon would be simpler and more visual. And it’s not hard to make, is it?
I would add to this the fact that in my country the time is changed twice a year. One hour back and one hour forward. One hour forward was just today. These things also add confusion even more.
That’s why it seemed to me that the best solution would be visualization through an icon that can be turned off/on at the player’s wish. It was also more convenient for clans whose players are from different time zones.