If you want this the fast and easy way, you have to get 10 people together because the online is as good as dead.
Have all people be mages and one of the losing team will use Meteor Storm on his team so they lose immediately. This way every round will take 15-20 seconds, and the game will last about 1 minute .
In Blitz mode you can choose the map you like the most, I recommend Wayland Keep or Deep Forest to do this because you can get to the other base really fast in case 1 person survives.
You can combine this achievement with the following:
Just have the winning team capture the flag every round as fast as possible and you'll win the match in about 3-4 minutes, giving you both achievements. Repeat for the other team.
Credits to WolfheartSpell to translate for my and FranDNK to help us find the solution.