Complex sentence: When they got the first pressing of a record they would play it to people they called the "old greys"-the collective nickname for the office cleaners who would typically start work at 5pm as office staff were leaving.
Split into simpler sentences: When they got the first pressing of a record they would play it to people they called the "old greys". An "Old Grey" was the collective nickname for the office cleaners who would typically start work at 5pm as office staff were leaving.