If you own a business, then taxes are due quarterly. See the form 1040ES instructions. If you just opened the business now, the next installment would be Sept 15 or so.
If you worked for someone else, taxes were probably withheld from your paycheck already. The normal time to file a return is by April 15th, but if you didn't make it, just get it in as soon as you can. If you were owed a refund, you might not need to file a return at all, but if so, you don't get your excess taxes paid back.