moment.now = function () { return +new Date(); }

If you want to change the time that moment sees, you can specify a method that returns number of milliseconds after unix epoc (1st Jan 1970).

The default is:

moment.now = function () {
    return +new Date();
}

Its used for moment(), and current date used when tokens are omitted from format. In general any method that needs the current time uses that at the lowest level.