Planning to head up towards Plum Island tonight and thought I'd maybe try the flats. Any suggestions as to what might be a good lure? Also, is it a better spot on the incoming or falling tide? Any advice would be much appreciated. Thanks.

If you are going to access by foot your best bet is to start wading out onto the flats about half way into the dropping tide. You can then continue to move around until the tide turns. Once the tide turns it is best to plan on being back off of the flats around half way into the rising tide. This way you are assured of not getting wet.

Points of safety out on the mud flats. It is easy to lose track of where you are (big place) bring a compass. Not such a big deal if it is a clear night but if the fog comes in it is a handy tool.
Also I have found a small red light pinned to a hat or suspenders is very useful. If it blinks it is even better. This lets other people know you are there.

With regard to plugs, surface swimmers, poppers, bombers and anything eel-like is a good bet.

Thanks for the advice. I've got waders. How much longer would that give me on the rising tide before I have to get out?

I was already assuming that you were wearing waders.