For Primary or Secondary schools, whenever a student XML file is imported, it is recommended that you tick "Start date for new students". Either keep the default start date that is automatically shown, or change it to the date on which you are importing this file.
Setting the End Date will depend on whether you are a Primary, Secondary or P-12 school.
For Primary schools, you should always tick on the End date for students not in XML file option and either leave the default date or change it to the date which you are doing the import.
For Secondary and P-12 schools, you should not tick on the End date for students not in XML file option as this will affect year 11 and 12 students who are generally not part of your XML file. If you need to end date students, you can create a Students CSV file which contains the students end dates and import this file instead. When importing the Students CSV file, do not tick on either the start or end dates.