Markets in America will generally be closed from 1pm. This includes the New York Stock Exchange and NASDAQ.
Stock market holiday closures: Crypto tends to correlate closely with the traditional stock market. So when markets are closed for holidays, Crypto trading activity usually slows down as well. That can lead to reduced liquidity with lower trading volume which can result in increased price volatility.
More information about how traditional market opening times are correlated with Crypto can be found here.