Halliday & Matthiessen (2014: 484):
Nominal conjunctions include in case, in the event that, to the extent that, and the + various nouns of time or manner, e.g. the day, the moment, the way. These last have evolved from prepositional phrases with the enhancing clause embedded in them, e.g. on the day when we arrived; but they now function to introduce hypotactic clauses just like other conjunctions, e.g. their daughter was born the day we arrived, the way they’re working now the job’ll be finished in a week. One clear indication that such constructions have been reanalysed from nominal groups with embedded clauses to nominal conjunctions introducing hypotactically dependent clauses is that the former ‘nominal groups’ no longer have the potential for modification; thus while we can say on the beautiful day when we arrived, it would be odd (or impossible) to say their daughter was born the beautiful day we arrived.