When adding an "accrual" (or length of service) timeoff type, there are three options to control when that accrual allowance will get applied.
The default option is Start Date Anniversary where it gets applied at each anniversary of the employee's start date.
For example, assuming we are looking at the allowance on 08/03/18 and the accrual type is setup to give 1 day per year up to a max of 3.
If an employee had started on 04/01/2016 then on 01/04/2017 they would get 1 day, on 01/04/2018 they would get another day giving a total of 2 as of 08/03/18.
The second option is Next Date - this opens up two additional drop-downs where you choose a day and month.
In the above example of starting on 04/01/2016 and using this with 1st January (entered as 1/1) as the date, the employee would get one additional day on 01/01/2017 and another on 01/01/2018 so again a total of 2 on 8/3/18.
The last option is Next Date + 1 Year - this also opens up the two additional drop-downs where you choose a day and month
Using the same example of starting on 04/01/2016 and, again, using this with 1st January (entered as 1/1) then the employee would get one additional day on 01/01/2018 only so a total of one in this instance.
This is because the rule is saying only give the employee their accrual allowance starting on the next 1st January after their start date plus one year.
Please note: In many cases the first and second options will actually be very similar and, if anything, the Next Date option may mean employees get service leave considerably quicker than using the Anniversary method.