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Calculating with time (JS), time format as HHMM

I'm in a brain freeze here.
I have 2 times:
(int) 1815 (18:15) and (int) 1915 (19:15) and I want to calculate the amount of 15 minute blocks between them. (4). How can I approach this in a solid manner?

You could take the minutes of every value and get the delta divided by a quarter hour.
function getMin(t) {
return Math.floor(t / 100) * 60 + t % 100;
}
var a = 1815,
b = 1915,
delta = Math.round((getMin(b) - getMin(a)) / 15);
console.log(delta);

Javascript setcookie()

The following line of code sets an event to happen only once per 24 hours, how do I make it occur every 12 or 6 hours? Thanks
setCookie(1, 24 * 60 * 60 * 1000);

JavaScript references time in milliseconds, and so therefore the equation 24 * 60 * 60 * 1000 is converting 24 hours into milliseconds (24 hours * 60 minutes in a hour * 60 minutes in a second * 1000 seconds in a millisecond).
Therefore, 12 hours would look like:
setCookie(1, 12 * 60 * 60 * 1000);
and 6 hours would look like:
setCookie(1, 6 * 60 * 60 * 1000);
and just for fun, 5 days would look like:
setCookie(1, 5 * 24 * 60 * 60 * 1000);

jQuery countdown date

I have this piece of JavaScript code I got from online and I am trying to modify itto countdown to July 10, 2013.
var currentDate = new Date();
$('div#clock').countdown(45 * 40 * 30 * 30 * 1000 + currentDate.valueOf(), function(event) {
July 10, 2013 is about 100 days from now so I want the days to show 100. I don't understand the format of how the date is being passed,I have tried messing around with it but it still doesn't work properly. I tried passing a new Date object to it but that doesn't work either. This code seems to be coming from this jQuery countdown library.

Instead of "45 * 40 * 30 * 30 * 1000" use "100 * 24 * 60 * 60 * 1000" so:
var currentDate = new Date();
$('div#clock').countdown(45 * 40 * 30 * 30 * 1000 + currentDate.valueOf(), function(event) {
would be the final code. That is 1000 (milliseconds/second) * 60 (seconds/minute) * 60 (minutes/hour) * 24 (hours/day) * 100 (days).

jquery date difference trouble

I made this little function from code snippets around the net. It does what its expected to do except that it decreased by 2 seconds every countdown tick instead of one, if i refresh the page it goes back to the original time again. Can you guys see what the problem is?
jQuery.countdown = function(selector, datevalue) {
var amount = datevalue*1000;
var curdate = new Date();
curdate = curdate.getTime();
var difference = amount - curdate;
if(amount < 0 || curdate >= amount){
$(selector).html("Done");
}
else{
datevalue--;
var daysRemaining = Math.floor(difference / 1000 / 60 / 60 / 24);
var hoursRemaining = Math.floor(difference / 1000 / 60 / 60 - (24 * daysRemaining));
var minutesRemaining = Math.floor(difference / 1000 / 60 - (24 * 60 * daysRemaining) - (60 * hoursRemaining));
var secondsRemaining = Math.floor(difference / 1000 - (24 * 60 * 60 * daysRemaining) - (60 * 60 * hoursRemaining) - (60 * minutesRemaining));
$(selector).html(daysRemaining+':'+hoursRemaining+':'+minutesRemaining+':'+secondsRemaining);
setTimeout(function() {
$.countdown(selector, datevalue);
}, 1000);
}
};
$.countdown('.date', 1332239568);

Remove datevalue--;
What you're doing now is to count down to a specific epoch time datevalue. But, you are decreasing it by one second each tick. Meanwhile, current time passes in setTimeout so you are both moving in time forward and pulling the target to yourself.
Either keep the original curdate of first call, saved somewhere. Or remove datevalue--;.

Calculate number of weeks , days and hours from milliseconds

There were many similar questions around but none addressed this calculation. Using javascript i it is easy to find the number of milliseconds diff b/w 2 dates for ex:
var mil = Math.floor(new Date("1/1/2012") - new Date("1/7/2012"))
mil is assigned 518400000
to get weeks i would do below
var weeks = mil / (1000*7*24*60*60);
in the above example it exactly fits 1 week. For other possible inputs i would like to get output as ex:
n Weeks, y days , z hours
So i did mil % (1000*7*24*3600) to get the modulus and from the remainder calculate number of days. but astonishingly this was answer i got from console
1 weeks , 6 days seems the week calculated before is also accounted for days again.
How should i calculate these correctly?

var seconds = (mil / 1000) | 0;
mil -= seconds * 1000;
var minutes = (seconds / 60) | 0;
seconds -= minutes * 60;
var hours = (minutes / 60) | 0;
minutes -= hours * 60;
var days = (hours / 24) | 0;
hours -= days * 24;
var weeks = (days / 7) | 0;
days -= weeks * 7;
Assuming mils is non-negative, this leaves mils in the range [0, 1000), leaves minutes and seconds in the range [0, 60), leaves hours in the range [0, 24), and leaves days in the range [0, 7).

There should be 6 days between them, not one week. Your weeks calculation needs to round down:
var weeks = Math.floor(mil / (1000 * 7 * 24 * 60 * 60));
Also, your milliseconds are negative; you want either
var mil = new Date("1/7/2012") - new Date("1/1/2012");
or
var weeks = Math.floor(Math.abs(mil) / (1000 * 7 * 24 * 60 * 60));