It is very cold in the city this week. Being on the ferry will be bitterly cold, so if you are going to do it, make sure to dress for it.

Carriage rides start I believe at a half hour, and you can increase the time. if it's under 20 degrees, they usually don't operate.

Tomorrow it may actually get a few degrees above freezing. It should be sunny and clear though.

You can do an express pass at the Empire State Building, where you go to the front of each line. I don't know if that actually saves any time or not.

I always tell people to experience Grand Central during one of the rush hours, either when everybody is arriving in the morning or leaving in the evening. It's much more impressive when the 750,000 people are passing through (at least to me).