Complex sentence: Although work was plentiful, the pay was poor and during the day he worked for his father as a sheet metal worker, a job that lasted for 12 years, during which time he made a few recordings for various small labels.
Split into simpler sentences: Although work was plentiful, the pay was poor and during the day he worked for his father as a sheet metal worker. This was to last for the next 12 years, during which time he made a few recordings for various small labels.