When I am converting date using strtotime() function it automatically added 1 hour in existing date.
For example:
$PublishDate = "1/13/2012 **17**:0";
echo strtotime($PublishDate);
// OUTPUT : 1/13/2012 **18**:0
Why 1 hour is incremented automatically?
Something odd is going on here. strtotime() converts attempts to convert a string representation of a date to the Unix time format (see the strtotime() documentation). Unix time is the total number of seconds since January 1st, 1970. This ends up being a large number, such as 1326723022 (the current Unix time as of writing). You can read more about Unix time here.
strtotime() should ALWAYS return either a 32 bit integer or FALSE (-1 in older versions of php).