From: http://www.tax.gov/calendar/

Tax Calendar - SB/SE
www.tax.gov/calendar/
Tax Calendar for Businesses & Self-Employed ... EFTPS users: Payments must be scheduled by 8 p.m. ET 
at least one calendar day before the tax due date. ... Fr, 15, Deposit payroll tax for Dec 2015 
if the monthly deposit rule applies.