Inferno tactics.

if you have a Fire Expert and a decent army that isn't just composed of Ifrits, you can first cast a mass fire resistance spell... and then cast Armageddons as long as you have the mana and health.

Seeing this, there's a good chance you'll get a mass dispel... But in general, you shouldn't drag it out; attack within 3-4 weeks. Invest everything in early guild construction and Ifrits. Also, invest in leveling up ONE hero so that they can deal as much damage as possible with their first cast.