I would strongly advise trying to improve the GMAT before applying. When you weigh the delayed application with the GMAT, you are better off waiting, because a 580 will hurt you applying to that kind of program. It would be best if you can break 700, but either way you should wait because a 580 could be a red flag.
good luck! Look at the Manhattan GMAT books
--Free application strategy discussion & initial essay review
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