You might want to ask the bank how long they guarantee the tank to be frozen for using the dry tank. I am pretty sure that Xytex uses the dry tanks and they were good for at least 7 days before needing to be recharged. I think this is a pretty conservative estimate just to cover themselves since when we recharged ours after a week, the vapors were still coming out and everything was still nice and frozen.
As a side note... I searched dry nitrogen shippers and came across a dog breeding site that sold the tanks http://www.majesticgaits.com/mve.htm
. For their dry shippers the least holding time was 14 days and most were around 21. Some of them look very similar to the one we got from xytex. So I think you should be fine to wait at least a week from when they ship out to recharge and not have to rush out. Did you find a place that would be able to do it for you? We used an oxygen supply company called Praxair. I looked it up and it does appear they have locations in MA, just not sure if there's anything near you.