Please consult http://labelary.com/zpl.html for general information about ZPL.
To test your ZPL label, use the API to create the label with an order and export as a ZPL file. Using the file, copy the information in this ZPL reader BinaryKits.Zpl.Viewer.WebApi (binarykits-zpl-viewer.azurewebsites.net) to make sure that the label is valid and comes out as you wanted.
Please note that if you are looking to add the date and time at the time of the label generation, you can use the following:
@System.TimeZoneInfo.ConvertTimeFromUtc(System.DateTime.UtcNow, System.TimeZoneInfo.FindSystemTimeZoneById("Eastern Standard Time")).ToString()