There's no harm in using carb heat more often, and I've been told if you think you have icing, you need at least 30 seconds each time. But in such conditions, every five minutes sounds like a good ide.? Why not? You don't need the extra power, unless you're about to do a go-around or similar. All it does is burn a very little extra fuel, and it may save your life.
Or is there something here I don't know about?