Not a silly question at all Michael! From what I saw on the IRS website, the due date schedule is as follows:
Time
Quarter 1 (Jan.1-Mar.31) Payment due Apr. 15th
Quarter 2 (Apr. 1-May 31) Payment due Jun. 15th
Quarter 3 (Jun. 1-Aug. 31) Payment due Sept. 15th
Quarter 4 (Sept. 1-Dec. 31) Payment due Jan. 15th of following year
