here is a snipet from php.net on the date() function for future and past events:
$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);