Lumia 520 supports 5 min maximum timeout due to the poor screen technology used (considering it's a budget oriented phone ) where as my lumia 920 shows never. But I have enabled glance screen to set to enable when the charger is connected (glance screen is not supported on lumia 520 again due to poor screen. )
Thanks for your replies. It seems odd that the Here app can keep the screen on all the time when the phone is being charged in the car but other apps (i.e. xbox music can't).