Look up the Date function in the PHP manual. Use it and MkTime() to find the time in the future.
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It is possible to use date() and mktime() together to find dates in the future or the past. Example 3. date() and mktime() example
$tomorrow = mktime (0,0,0,date("m") ,date("d")+1,date("Y"));
$lastmonth = mktime (0,0,0,date("m")-1,date("d"), date("Y"));
$nextyear = mktime (0,0,0,date("m"), date("d"), date("Y")+1);
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