One of the big reasons games last so long is because it seems that the time estimation is based on people playing the game appropriately. I don't mean to be flaming people, but... if you are...
A) Pressuring towers early and often
Spending gold on team wide upgrades... new creep units, more creep damage/armor, building upgrades
C) Build your team with a good cohesion of characters (ex: Sedna for support/healing, UB for DG/tower, TB for creep/DG killing)
The listed points seem to be what I have discovered leads to very short games, my fastest 2v2 was ~10 minutes. My friend and I (UB/Sedna) put constant pressure on enemy towers while one of us upgraded creeps/team upgrades and the other bought more equipment to keep ourself up and running. The UB's ability to bring down towers and pressure DG's along with Sedna's ability to keep us moving forward and never have to reach brought us to victory fairly quickly. I am definitely looking forward to see how competition may shape up in this game. 