That's simultaneous submissions. I've always believed it's a bad idea, unless you're trying to build a large stack of rejections. Sim subbing gives you no chance to change a story before you submit it to the next market after one rejects it.
Really good stories do not need to be sim subbed, and bad stories stand no chance of getting better when you sim sub.
Too many writers worry about time. The notion that you should sim sub because it takes a long time for some magazines to report just doesn't hold up. Simply put, a slow acceptance is a heck of a lot better than twenty fast or slow rejections. Better that it takes three years to sell a story than to receive twenty rejections for that story in six months.The way you beat the time factor is by writing and submitting more short stories. Do this, and it won't be very long before you're hearing back from one magazine or another on a regular basis.
And when a story is rejected, you have teh chance to make change according to any feedback you receive before sending it out to teh next market. If your stories are any good, anywhere near pubishable quality, you will receive feedback from editors.