This is practically guaranteed on Soul Attack Advanced.
Your best bet is to use a character you have leveled fairly high AND that you are extremely comfortable with in regards to building a crazy high slash combo. It doesn't have to be a maxed out character, but one with most of the wonderful bells and whistles that are available is definitely going to be helpful.
Do not concern yourself too much with the timer here - if you know what you are doing, and are using a decent, leveled character, then you will lay waste to everything leaving that timer an insignificant annoyance.
I did this with a leveled 160 Nnoitra - the guy is a combo beast. His triangle moves are some of the best in the game for building crazy high combos AND dealing damage to bosses.
The goal here is to get your combo counter up to 1k+ quickly, and keep it there throughout the entire mission. Seems daunting, but it really isn't. Anything can be used to keep your combo up: enemies, environmental objects, and those crystals that give you wonderful items all keep your combo going.
A combo above 1k gives you x4 soul points. This means all those normal enemies that give either 2 or 4 soul points per kill are now up to 8 and 16. Doesn't seem like much, but when you are in a group of 30 enemies...
30 x 4 = 120
30 x 16 = 480
(math is fun!
Tougher enemies, and bosses, deal out even more soul points, so going into a boss battle with a high hit counter, and not backing off said boss, will dish out an awesome bonus when everything is said and done.
In Soul Attack Advanced there are A LOT of enemies to take on, so don't think you will be short on baddies to keep that counter full. Also, remember that those wonderful environmental objects (trees, buildings, gas tanks, etc) also deal out soul points, so hitting them whenever you can will not only keep that hit counter full, but also give you the soul points x the multiplier.
If your ignition gauge becomes full, use it, BUT DON'T USE THE SUPER MOVE!
The ignition state boosts all your attacks, and as long as you are defeating enemies, and keeping your combo high, then your ignition state will keep refilling itself - essentially it will never run out!
Lastly, there are a few bosses to deal with here (
). The first actual boss (I believe) is Rudbornn (or Rudbon, I don't remember
). Shortly after that you end up in an area with a center room, and four other rooms branched off. Every room, save one, has a boss, but they all have enemies. You will need to fight Stark, Halibel and Barragan. After the four rooms are cleared you will be fight Aizen (half awakened).
As always, if I missed anything please leave a comment below.