What part of NJ? Check Bill's zone chart, zone is important...I'd soak 'em overnight and plant...if they freeze, replant...early is good. They are a warm season crop, though, so you could wait if you must.
I would make a good guess of the first week of May being fine. In MN I plant beans early May which is before the last frost date but they are always fine.
Gardening in March
Gardening in April
Gardening in May
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