Hi Percy
You'll have fantastic time in New York and Boston. I've been to both (though not at Christmas) and found them fascinating. Boston is one of the US's oldest colonial cities, while New York is of course high-tech and very modern.
It will be cold - about 5 or 6 degrees celsius - but wrap up warm and you'll be fine. The US East Coast is 5 hours behind the UK. For more information, have a look at the tour on our website and click on the grey 'country e-guide' option. You'll find everything you need to know there.
Kind regards,
Olly, your editor