You can get the train schedules (below) from the NJ Transit Site. 

There is a 6:01 out of NY Penn Station that will get you into Matawan around 7:00 pm.

I don't recommend the 6:13 as it looks like you would have to change trains in Newark. (That's not a bad thing, of course, but since I hate to change trains, I am assuming you will too.)

If you can't catch the 6:01, you're better off waiting for the 6:32. See the schedule for other options as well.

Since the party goes til midnight, though, you may want to catch the 11:59 out of Aberdeen Matawan. 

The last train back to NY is 12:49 pm.

From NY Penn Station to Aberdeen Matawan for Fri Oct 21

Return Trip: From Aberdeen Matawan to NY Penn Station for Fri Oct 21

To enlarge the images below, hover your mouse over the lower, right-hand corner. Click the magnifying glass that will display to enlarge the image for optimal viewing.

 When you return to NYC, be careful not to get off at Penn Station Newark in NJ.