Many small business owners looking for a tax break for 2011 still have time. Tax returns for 2011 are due next week, but the Internal Revenue Service has liberal deadlines for contributions to many retirement plans. A contribution for the prior year must be made by the due date, Tuesday, April 17. You can get even more time if you’re planning to file for an extension. In that case, you have to make the contribution by Oct. 15 and you don’t have to pay a penalty or extra tax. Many small business owners get extensions routinely so they have more time to make their retirement plan contributions.