Complex sentence: It is quite clear that Verdi's characteristic requirement for brevity appeared this early in his career, but his health forced a postponement until at least following August, although he was well enough when he arrived in Naples by the end of July to oversee rehearsals.
Split into simpler sentences: It is quite clear that Verdi's characteristic requirement for brevity appeared this early in his career. He was well enough when he arrived in Naples by the end of July to oversee rehearsals.