Most I ever ran mine was 40 minutes. It was -6F. When I went to start it, the temperature was at normal running temp. It fired right up with a 15 second hold on the glow plugs.Rather surprised that you didn’t plug it in for about an hour before attempting to start it.
My LS is stored in unheated building but if the temperature is much below freezing I’m happy to plug it in for awhile before attempting to start it, when it’s below zero I plug it in hours ahead of time