Sets a string that indicates the date and time when the file was last written to.
fileInstance.LastWriteTime = newLastWriteTime
|string||newLastWriteTime||The date and time when the file was last written to.|
file f = new file("c:\somewhere...");
f.LastWriteTime = "3/04/2016 4:13:00";
It's a wrapper of the System.IO.FileInfo.LastWriteTime property.
The date and time string is converted to the C#'s DateTime type by the System.DateTime.Parse(String) method.
Links for reference