When is anybody's guess. If you insist on taking ill-advised advantage of this voluntary at your own discretion as an employer program, I would suggest a temporary workaround.
Run payroll as normal with the employee SS being calculated AND deducted. Add an after tax payroll addition (similar to employee advance) equal to the 6.2% . You can make adjustments later.
Keep in mind that you as the employER are still ultimately LIABLE for submitting this deferral. Th eIRS even says so directly and as a matter of fact when it describes the "affected taxpayer" , which are employers, not employees.
Meanwhile if you utilize Direct Deposit you have until 5:30 PM Pacific Time to upload your payroll for this Friday