Question 1: What are the ITDs corresponding to these IPDs for each frequency?
500-Hz tone:
A full cycle (360 degrees) of a 500-Hz tone has a duration of 2 ms.
So a phase difference of 45 degrees corresponds to a time difference of (45/360)*2 ms = 0.25 ms.
2000-Hz tone:
A full cycle (360 degrees) of a 2000-Hz tone has a duration of 0.5 ms.
So a phase difference of 45 degrees corresponds to a time difference of (45/360)*0.5 ms = 0.0625 ms.