You can find the Hour of Twilight dungeon within Caverns of Time, Tanaris.
The coordinates are (64.3,49.5)
/i Dispel Chains of Frost. Avoid the Ice Boulders that land (circles under feet). Destroy the Icy Tomb to free Thrall. At 30% boss casts Torrent of Frost (does high damage & slows movement), use bloodlusts, cds here.
2. Asira Dawnslayer
/i Tank kite boss out of Smoke Bombs, try stay close to Thrall for totem buffs. Random spellcaster will get Mark of Silence, avoid silence by standing behind tank or melee (so knife hits them instead).
3. Archbishop Benedictus
/i Dispel Righteous Shear/Twilight Shear. Purifying Light/Corrupting Twilight forms 3 orbs, spread out for this then move out of pool. Move away from Wave of Virtue/Wave of Twilight. (Twilight spells are cast when turns into shadowform at 60%).