The initial measurement period is used for new variable hour, seasonal, or part-time employees.
It can begin on the employee's start date or on any date up to and including the first day of the first calendar month following the employee's start date.
If you're using payroll periods for your measurement periods, it can also begin on the first day of the first payroll period starting on or after the start date (even if it begins after the first of the calendar month after the start date).
The employee's hours of service are measured during this period. If the hours of service are an average of at least 30 hours per week, that employee will be treated as a full-time employee during the following stability period associated with the initial measurement period.