Names the whole festive stretch that follows lunar New Year's Day, not a single date, and it is the word greetings reach for: 新春快乐 and 恭贺新春 fill couplets, cards and shop windows, where the plain 春节 would read as a calendar label.
usage
The literal sense, early spring, still exists but is a written, poetic use. In ordinary speech 新春 means the new-year period and nothing else.