I might be able to shed some light on this, and I could be wrong, but based on my experience ordering seeds here's what I think is going on.
I think it's actually NOT sitting in customs to be "cleared", I think they are just slow and behind (or short staffed) in New York.
Here's why I say that. I ordered from another place, via registered mail, and it shipped from the UK on January 19. Six days later, on the 25th, USPS tracking information updated to say it arrived in New York on the 21st. This made me think it arrived in New York on the 21st., but sat in a container or something, and didn't get scanned until the 25th., but showed the 21st because that's when it did in fact arrive in New York.
My packaged got delivered to me on the 29th, EIGHT days after it arrived in New York. My "package" was a thick envelope, so it wasn't a box type package, so it's nothing they would normally inspect, it was more like a letter.
So depending where you are in the U.S., it should be any day now, and too, take into account that New York has been creamed with massive snow, and the north east has been shut down at times over the last few weeks, which may also be playing a part.