To further expand on what Zoap is saying, here's the deal with time...
Each game should take about 5 minutes, unless one of the players is really bad. At this point in the game, most of the people who enter tournaments are pretty decent, and won't get themselves killed so easily. Any match containing one or more of Samus, Peach, or Jigglypuff will easily go longer than 5 minutes assuming non-suckage.
You gotta decide how hardcore you want to be in running a tournament. When people get eliminated they usually want to play casuals instead of watch, which not only takes away TVs but can distract people who are still in the tourney. This makes it harder to find people for their matches. Even without any casuals allowed you still have to find people and people have to setup for their match. You also have to consider if someone wants to watch the last round of another match or something like that.
The number of TVs you can use gets low pretty quickly. Often times a bracket will become stilted due to a few matches ending really quickly and a few more going longer. This isn't really a problem per se, but it does mean that the tournament will last as long as the longest matches in a group, because those need to finish in order for the rest of the brackets to move on.
Not to mention other common things like bathroom breaks, eating, resting in general, discussion of rules, judgements if a dispute comes up, power failure, etc.
Also not discussed at all is the time it takes to set up a bracket. You could do it all randomly, but most people appreciate it if you separate them from the people they came with to the tourney. You don't want to pay money just to play against the people you play with all the time anyway, unless it's the finals. It's also nice to do some general seeding, but that's not always easy.
Still, it is possible to run things exceedingly smoothly, in which case a 2-3 hour tourney could still be possible. You just have to run it harcore, and hope things turn out right.