When you configure PSA to use the show schedule grid option, you must ensure that users have read permissions on the schedule object. When you configure PSA to use the schedule editable option, you must configure Insert and Delete permissions on the Schedule Exception object.
The data that populates the Schedule Grid is retrieved using sharing. Salesforce's sharing rules are applied where only records display that users have permission to view. You may need to set up sharing rules and other record sharing techniques to ensure timecard users can view appropriate schedules. For more information, search for "Sharing Rules" in the Salesforce online help.