Hi johno welcome to the site.
Have you got the console switch for the heating/ventilation switch set correctly,If you have it set to widscreen,it will come on,if you turn it so the air flow is through the vents,it should go off & only come on again when you push the dash button for it.
As to the instrument panellight to stay on,yes it is normal but not usually for that long.
As you have a 58 plate model,there may be a knob to set the length of time it is on for.Have a look through your handbook.I have a 53 plate Zetec & I dont have this but the light stays on for between 1 2 mins.
MetalMicky ( Mike)
2004 2.0 TDCI Zetec