Regarding travel time:
The express train from Princeton Junction to NYPenn station would take 1 hour. Then you'd have to transfer to subway to get to wherever you work so it would take at least 1.5 hour door to door.
Regarding parking at Princeton Junction:
If you have to be at work THAT early, you may be able to find a daily parking spot at Princeton Junction (this is different from the parking permit that takes 3-5 years on the waiting list). I've heard that the daily spots fill up around 6:30am and it's $5/day. West Windsor Parking Authority
Other options would be living in apartment complexes that offer shuttle service to/from the train station and carpooling to the station.