It can be a bit confusing particularly because of the tax act passed in late 2017. Last year there was good reason to install the TTU right away, change the FICA limit etc, before printing the W2 if the W2 is printed after the first or second payroll. The tax changes affected the withhholding significantly and some customers wanted the lower withholding reflected on the first payrolls of the year to keep employees from complaining.
Realistically, installing the TTU in Feb and being a bit over withheld never hurt anyone.