I'm not sure about Normal/Heroic/LFR, but I know for a fact Mythic Hellfire Assault, which is still very difficult to solo and having accurate timers would make so much easier, is completely mistimed.

A year later but this is still an issue. Its such a PITA to solo this without knowing where mobs are spawning next.

As the way this module is created, it will not speed up as you do the fight faster; I assume waves come earlier as you clear them. Thus timers will be off unless you leave 1 npc alive and wait for the next wave to spawn.