The  Fire  Knight  team  I  use  is  following:

-  Arbiter

-  Stag  Knight

-  2x  ColdHeart 

-  Mortu  Macaab

My  best  time  is  2:11.

I  think  to  improve the  time  we  would  have  to  kill  faster.

We  would have  to  use  a  Nuke/Reset  Strategy.

Royal  Guards  dont  work  on  Fire  Knight  due  to  Affinity.

I  think  we  would  have  to use:

-  Zavia  /  Poison  Explosion  Team

-  Seer  /  Mage  Buff  Strip  Team

We  would  have  to  clear  waves  in  20-30  seconds.

We  would  have  to  clear  boss  in  20-30  seconds.

It  should  put  our  clear  time  around  40  second  to  1  min.

You  don't own  Zavia.

You  don't  own  Seer.

I  question whether  or  not  you  have  the  ability to  improve  your  time.

It  is  a  real  shame.

I  find  myself in  a  similar situation.

I  have  thought  about  using  a  Rally  Champion  on  my  Team.

The  problem is  I  dont  have  any  leveled.

Have  you  tried  using  a  Rally  Hero  on  your  team?

yes but the time is similar/worse than the one of a team with counter atk. 

I also tried both - counter atk and ally atk together but the result was pretty shameful aswell :(

Guess I will stick with the 2 min time :( 

If i had second coldheart it would be faster on the boss but im not sure about waves. but on the other hand i wouldnt need counter atk when 2 coldhearts can almost clear the shield.