JavaScript version of this ruby: http://project.ioni.st/post/2288#snippet_2288

gistfile1.js

Date.prototype.atSomePoint = function(hours) {
	var startHour = new Date(this.valueOf());
	var endHour = new Date(this.valueOf());
	startHour.setSeconds(0);
	startHour.setMinutes(0);
	endHour.setSeconds(0);
	endHour.setMinutes(0);
	if (hours) {
		startHour.setHours(hours.between);
		endHour.setHours(hours.and);
	}
	else {
		startHour.setHours(0);
		endHour.setHours(24);
	}
	return new Date(rand(startHour.valueOf(), endHour.valueOf()));
};

Number.prototype.am = function() {
	return this;
};

Number.prototype.pm = function() {
	return this + 12;
};

function rand(lowerBound, upperBound) {
	return Math.floor((upperBound - (lowerBound - 1)) * Math.random()) + lowerBound;
}

new Date().atSomePoint();	// Fri Jul 25 2008 15:22:15 GMT-0400 (Eastern Daylight Time) 
new Date().atSomePoint({between: (1).am(), and: (7).am()});	// Fri Jul 25 2008 04:24:29 GMT-0400 (Eastern Daylight Time) 
new Date().atSomePoint({between: (1).pm(), and: (7).pm()});	// Fri Jul 25 2008 17:14:38 GMT-0400 (Eastern Daylight Time)