Help with backing up a folder

I am trying to move a directory to another directory, here is the code:
My.Computer.FileSystem.CopyDirectory("C:\Users\User\Desktop\sections\login\login", "C:\Users\User\Desktop\back up\" + DateString + TimeString,
FileIO.UIOption.AllDialogs, FileIO.UICancelOption.ThrowException)

I have tried it without datestring + timestring and it works but once I inputted this into the program I got the error "The given path's format is not supported."

How do I work around this so that it saves in this directory with the file name being the date and time?