This function finds the user's local date/time converted from EDT at a set time in the future. Useful for expiring cookies on a regular basis. By default, expires cookie once-per-day at 12:01 AM EDT the next day, every day. Modify offsets accordingly.

expireCookie.js

function findLocalExpTime() { 
	var curTime = new Date(),
		expTime = new Date(),
		baseZoneOffset = 4,	// Base timezone offset from UTC (4 in this example for EDT, change as appropriate)
		tmpYear = curTime.getUTCFullYear(),
		tmpMonth = curTime.getUTCMonth(),
		tmpDate = curTime.getUTCDate(),
		tmpHrs = curTime.getUTCHours(),
		tmpMin = curTime.getUTCMinutes(),
		localTime;

	if (curTime.getUTCHours() > baseZoneOffset || (curTime.getUTCHours() == baseZoneOffset && curTime.getUTCMinutes() >= 1)) {
		expTime.setUTCFullYear(tmpYear,tmpMonth,tmpDate+1);
		expTime.setUTCHours(baseZoneOffset,1,0,0);
	} else {
		expTime.setUTCFullYear(tmpYear,tmpMonth,tmpDate);
		expTime.setUTCHours(baseZoneOffset,1,0,0);
	}    
	
	localTime = new Date(expTime.toUTCString());

	return localTime;
}