The IRS has released IRS Notice 2013-14, which provides transition relief given the late retroactive renewal of the Work Opportunity Tax Credit program in January. The transition rules are not the same, however, for all WOTC target groups.
Notice 2013-14 waves the 28-day deadline for submitting IRS Form 8850 (the WOTC Pre-screen Notice) for qualifying employees hired within certain dates ranges in 2012 and early 2013. The extended deadline for submitting the applications for affected employees is now April 29, 2013.
The rules apply as follows:

• For all targeted groups except qualifying veterans, the extension applies to qualifying employees hired from January 1, 2012 through March 31, 2013 (that’s a period of 15 months).
• For qualifying veterans, the extension applies to qualifying employees hired between January 1, 2013 through March 31, 2013 (a period of just 3 months)

Excerpted from Notice 2013-14
 Targeted Groups other than Veterans:

A taxable employer that hires a member of a targeted group (as defined in § 51(d)(2) through (10), other than a qualified veteran described in § 51(d)(3)) on or after January 1, 2012, and on or before March 31, 2013, will be considered to have satisfied the requirements of § 51(d)(13)(A)(ii) if it submits the completed Form 8850 to the DLA to request certification not later than April 29, 2013.

Qualifying Veterans:

An employer that hires any qualified veteran described in § 51(d)(3) on or after January 1, 2013, and on or before March 31, 2013, will be considered to have satisfied the requirements of § 51(d)(13)(A)(ii) if it submits the completed Form 8850 to the DLA to request certification not later than April 29, 2013.

Here a link to the entire Notice 2013-14.