Burn Time: How Long Does It Last?

Hello!
"When I look at Group 12, Field 2 in the diagnostic values for my small 1.4 TDI AMF engine, the value displayed under 'glow duration' for the current outside temperature (around 0°C) is 3.93. What unit is this value in? Is it a time unit, like seconds? It seems too low for a time value, because I have to preheat for longer before the control light goes out."
Maybe someone can tell me something about it.

thank you
brezelmann01