how much time is needed from the time i park til i get to terminal? if i have an 8pm flight , what time do i need to allow for parking and getting to the depature gate?

I would say keep 25 to 30 mins to get from parking to security checkpoint at the Newark Airport. I would say they are pretty prompt in picking you up on a shuttle to airport with almost no wait time. Security may take anywhere from 20 to 40 mins depending on rush, whether or not you have TSA pre-approval, etc.

1-1/2 to 2-hours

Boarding time is usually 1/2 hr. - 40 min. before departure, parking to security can take upto 1/2 hr., getting thru security can take another 1/2 hr., if u r unlucky longer.

I always leave 90 minutes. I'm never at the parking lot for more than 5 minutes

I suggest you always set your self a two hour window jus for traffic and parking being congested