Barely. I think you can always use 'ertussen'. But you use 'hiertussen' only when you are mentally or physically really pointing to the things (between which there are several years). It has a bit more emphasis.
I felt like I was sort of grasping the difference between "ertussen" and "hiertussen", but I can't figure out why the latter is the right one here. Could they both be used (I'm guessing not)? And if not, why?
To be be honest, this 'er section' is quite literally 'doing my head in' ! I am totally bamboozled.Been with it for nearly two weeks, and still no nearer to solving its intricacies. Almost sorry I started !