Generally SEPs can be set up and funded by the tax filing deadline. If an employer chooses to make an annual contribution into a SEP IRA on behalf of all of his employees, it must be made by the same due date as his Federal Income Taxes. In most cases, this is April15th, but if an extension has been filed, the SEP does not have to be set up until October 15th.
Because SEPs do not require continuous annual contributions, and because contributions can be added after January 1, they are very flexible and attractive to small businesses. Employees are even able to make traditional IRA contributions as part of a SEP arrangement.