so an easy way to see it is:
Delay - the amount of time it takes voice packets to get from 1 end to the other end. This is one way delay. Obviously, the more delay, the more noticable it is, and people will start to ‘talk over’ each other. Apperenlty less than 200 - 300 ms is not too bad, but that is debateable, each person is different.
Jitter is just the change in delay, so if jitter is high, voice packets are arriving at the other end in a haphazard way, some late, some on-time, so the vocie would be bad.
Not a direct answer, but you jitter should be constant, and delay < 200 ms.
However, these two are sometimes used interchangeably, so they might refer to the same thing, than jitter should be less than 200 ms.