Assuming you haven't run Period End or Year End in Receivables since you posted the cash batch, it's pretty straightforward to reverse the Cash batch.
Depending on how many checks are in the batch, you could either recover the posted cash batch (if you are using AR 9.2A) or just re-enter the checks as a new cash batch, using the same wrong date and in the negative, and then applying them to the same invoices you applied the original cash batch - again in the negative. Posting this batch will bring you back to square one, and then you can enter the checks a third time, with the right date.
When you re-enter the checks, use a slightly different check number, for example 12345A instead of 12345.
When you retrieve these into the Ledger, the reversed cash batch with the wrong date will offset the original cash batch with the wrong date, and you can safely delete them.
Make sure to make a backup before doing this; there is a moderate chance that things could get really screwed up if you are not careful.
Steve