How to check is timezone identifier valid from code?

I'll try to explain what's the problem here.

According to list of supported timezones from PHP manual, I can see all valid TZ identifiers in PHP.

PHP How to find the time elapsed since a date time?

How to find the time elapsed since a date time stamp like 2010-04-28 17:25:43 , final out put text should be like xx Minutes Ago / xx Days Ago

How to convert Milliseconds to "X mins, x seconds” in Java?

I want to record the time using System.currentTimeMillis() when a user begins something in my program. When he finishes, I will subtract the current System.currentTimeMillis() from the start variable, and I want to show them the time elapsed using a human readable format such as "XX hours, XX mins, XX seconds" or even "XX mins, XX seconds" because its not likely to take someone an hour.

jQuery FullCalendar timezone syncronization

I am using the jQuery Fullcalendar plugin (http://arshaw.com/fullcalendar). I am only using it for "full day" events. When the user creates an event, I store it in my database via php as a date (2012-01-12). When sending the list of events to FullCalendar via ajax I convert the date to UNIX time.