Final answer:
The pay structure described is time-based differential pay, where Amar is paid a different hourly rate depending on the time period he works.
Step-by-step explanation:
The pay structure described is time-based differential pay. This is because Amar is paid a different hourly rate depending on the time period he works. From 8 a.m. to 5 p.m., he is paid $27 per hour, but from 4 p.m. to 12 a.m., he is paid $32 per hour. This differential in pay based on the time worked is what characterizes time-based differential pay.