26 CFR §301.7508-1

1. (a)General rule. The period of time that may be disregarded for performing certain acts under section 7508 applies to acts described in section 7508(a)(1) and to other acts specified in a revenue ruling, revenue procedure, notice, or other guidance published in the Internal Revenue Bulletin (see § 601.601(d)(2) of this chapter).
2. (b)Effective date. This section applies to any period for performing an act that has not expired before December 30, 1999.