Iron Council (Steelbreaker Last): Overwhelming Power rules for countdown.
This should effectively count down how much time is left on your tanks' Overwhelming Power debuffs to your raid.
25 Man:
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 30 seconds.
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 20 seconds.;10
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 15 seconds.;15
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 10 seconds.;20
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 9 seconds.;21
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 8 seconds.;22
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 7 seconds.;23
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 6 seconds.;24
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 5 seconds.;25
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 4 seconds.;26
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 3 seconds.;27
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 2 seconds.;28
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target melting down in 1 seconds.;29
/tjh rule SPELL_AURA_APPLIED;;;61888;raid;RAID;*target dead.;30
10 Man:
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 60 seconds.
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 50 seconds.;10
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 40 seconds.;20
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 30 seconds.;30
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 20 seconds.;40
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 15 seconds.;45
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 10 seconds.;50
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 9 seconds.;51
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 8 seconds.;52
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 7 seconds.;53
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 6 seconds.;54
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 5 seconds.;55
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 4 seconds.;56
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 3 seconds.;57
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 2 seconds.;58
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target melting down in 1 seconds.;59
/tjh rule SPELL_AURA_APPLIED;;;64637;raid;RAID;*target dead.;60
Haven't tested these yet, and Iron Council is already dead for us this week, so it'll have to be next week. If it works as I'm hoping it does, though, it should make it clearer for everyone as to how much time is left and when tank transitions will be taking place.