How should I populate accrual "Months of Service" in the Accrual Plan setup?
In Admin > Setup > Accrual Plans, you may specify rates of accrual depending on length of tenure with the company. The "Months of Service" column on the Schedule tab means months of completed service. For example, if you allow people to accrue 10 hours per month for their first year and 13.333 hours per month for their second year, you would populate "Months of Service" with 0 for the first row and 12 for the second row.
As a comparison, you would not populate it with 13 as this field does not mean "month of service" (in your 13th month). It means completed months of service. Second screenshot below is how not to set it up.