There is this language in the preamble and then there is the debate about what "practicable" means...
The final rule, however, also recognizes that there may be circumstances when changes must be made within a time frame that precludes compliance with the 30-day advance notice requirement, such as the immediate elimination of an investment option when it is determined to be no longer a prudent investment alternative. In such cases, the rule requires that information be furnished as soon as reasonably practicable.