how to calculate the remaining time with php and mysql?


i have a situation where i need to calculate the remaining time every 6 hours, whenever i view the time.

i have this setup:

<div id="time"><div>

to be more precise i have a trigger that gets the time starter:

$(buttom).on('click', function(){
    ..... send through ajax the current time to a php file
    ...if success, get the response and place it in the div

in the php file i store that time to the database

if (isset($_POST['time'])){

what happens now is that whenever i view that div i should see the left time:

<div id="time">5h:50min<div>

i vizit again in 30 min i see

<div id="time">5h:20min<div>

and so on.

the problem is not sending the time back and forth using ajax or something, but sending the correct time.

What i was thinking is to send the time every time i visit the page. First time store it in a table field and the other times to store them in a separate table field

id     time1        time2
1      123456..     123124..

the time1 stays unmodified as it is the original time and every time i visit the page i send the new current time and update time2

here i get a bit lost.

this is how i get time1: $getTime = $data->getTime($userId);

and this is the time that comes in every time: $time

i also know that 6h is 21600 seconds


if ( $time >= ($newTime + 21600) ){
    //if the current time is bigger than the first time + 6h it means that 6h have passed
    // store the new time in the database for reference as the new main time
} else {
    // 6h have not passed yet and we need to calculate how much time is left
    //here i get confuzed


I know this post is a bit confuse maybe, but i hope its understandable.

any ideas?


If you're going to store the time for when you last visited the site you only need to store one time.

So for your example:

$current_time          = time();
$last_visit_time       = $data->getTime($userId);
$since_last_visit_time = $current_time - $last_visit_time;
$six_hours_in_seconds  = 21600;

if($since_last_visit_time > $six_hours_in_seconds) {
    // not sure of the function call here so using yours
    // store new time as it's been over 6 hours
    $remaining_time = $six_hours_in_seconds;
} else {
    $remaining_time = $six_hours_in_seconds - $since_last_visit_time;

echo "Remaining Seconds: {$remaining_time}<br />";

Part 2 using JavaScript / Ajax you can use this to display the remaning time



var time_in_seconds = 21600; // this would be the $remaining_time PHP variable

setInterval(function() {
}, 1000);

function seconds2time(seconds) {
    var hours   = Math.floor(seconds / 3600);
    var minutes = Math.floor((seconds - (hours * 3600)) / 60);
    var seconds = seconds - (hours * 3600) - (minutes * 60);
    var time = "";

    if (hours != 0) {
      time = hours+":";
    if (minutes != 0 || time !== "") {
      minutes = (minutes < 10 && time !== "") ? "0"+minutes : String(minutes);
      time += minutes+":";
    if (time === "") {
      time = seconds+"s";
    else {
      time += (seconds < 10) ? "0"+seconds : String(seconds);
    return time;


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