Completes the asynchronous operation started in BeginGetLastWriteTime.
Modification time of file as a DateTime.
Before calling BeginGetLastWriteTime, you need to create a callback method that implements the AsyncCallback delegate. This callback method executes in a separate thread and is called by the system after BeginGetLastWriteTime returns. The callback method must accept the IAsyncResult returned by the BeginGetLastWriteTime method as a parameter. This parameter may then be passed to the EndGetWriteTime method to complete the operation.