3 minutes feels like it's too short, it means you have only 2 well thought out, prepared, and executed attempts at breaking the other team's hold, 3 if you rush it a bit. The flip side of this is that on defense, you only have to hold 2-3 sac or push attempts from the other team to get a round reset to mid. At least at my level, if my team is holding last against an opponent that's about the same level as us, I'm pretty confident that we can hold against 2-3 attempts if we make no effort to countersac more than one player or push out. Extend that out to 3-5 attempts by extending the round timer to 4 or 5 minutes, and it becomes significantly more risky to just turtle.
If you cannot break a hold with 2-3 attempts I don't blame you, if you can't break it with 5 attempts you probably deserve to be reset to mid IMO, so my vote is for a 5 minute round timer.
Watching top Invite players take DM fights over and over *is* wildly entertaining, I must say, but as others have said, 3 minutes does remove some of the interesting depth of breaking a hold.
I do really like the "overtime until one team wins" aspect of the ruleset, and I think Fullerton demonstrated that running a proper tournament with it is possible even with potentially infinite overtime.