i thought the two of them not speaking started from the moment Hermoine tied her scarf around the trees (maybe even before that after she chased Ron out of the tent), to them apparatus to the new location and Hermoine choked down her tears, to Hermoine being in the tent and Harry sitting outside. All these time Harry’s worried about Hermoine and didn’t know what do say. Until when he heard the part of the Nick Cave song that said “O children, Lift up your voice, lift up your voice” and went over to put out his hand.
They started dancing and Hermoine didn’t really bring a smile until the part of the song that said “Children Rejoice, rejoice”.
And even during and after the dance the two didn’t speak to one another. It’s only till Harry discovered the “I open at the close” part that he spoke to Hermoine about it.
I see why it might have not driven home the point that those two were in such pain that they didn’t speak for a long time. but even more time spend on them not speaking would make that part of the movie very awkward.