September has no day 31. 
perldoc -f Time::Local

 It is worth drawing particular attention to the expected ranges for t
+he values provided. The value for the day of the
       month is the actual day (ie 1..31), while the month is the numb
+er of months since January (0..11). This is consistent
       with the values returned from "localtime()" and "gmtime()".

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Jan = 0, Feb = 1; Aug = 7; Sept = 8; Dec = 11.

In reply to Re: timegm: There is no August, 31 in 2009 by tlhackque
in thread timegm: There is no August, 31 in 2009 by Rabenschwinge

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