Allow users with proper RBAC Scheduling permissions (read/write for task actuals) to status Tasks -
Set status to Started or Finished.
For task status set to Started - let user input Actual start date and time, % complete
For task status set to Finished - let user input Actual Start date and time, and Actual finish date and time.
This functionality is not available in Field at all. There is no schedule view in Field, we cannot see planned/actual dates nor edit them.