The Time Sheets function within Importacular maps directly to the section of the same name on the Volunteer tab on the Constituent record.
Below, you can see the Importacular mapping area for Time Sheets.
The date is a required field and it is also a key field (meaning that, if it is not populated for any reason, the mapping will not import).
You also have Area Settings for Time Sheets. These allow you to determine what constitutes a match between the data in your source versus the data in Raiser’s Edge and what you would like to do when the data matches (add anyway, update the existing time sheet or leave the existing time sheet in RE as is).