See Time::Local, emphasis by me:

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

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

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