27 CFR §70.210

1. (a)Time for bringing judicial action. An action for judicial review described in 26 U.S.C. 7429(b) may be instituted by the taxpayer during the period beginning on the earlier of:
   1. (1)The date of the reviewing officer notifies the taxpayer of the determination described in 26 U.S.C. 7429(a)(3); or
   2. (2)The 16th day after the request described in 26 U.S.C. 7429(a)(2) was made by the taxpayer; and ending on the 90th day thereafter.
2. (b)Extension of the period for judicial review. The U.S. Government may not seek an extension of the 20-day period described in 26 U.S.C. 7429(b)(2), but it may join with the taxpayer in seeking such an extension.