A somewhat elaborate but thorough way to do this is to convert all of the dates to Unix/Perl timecode values. This will allow you to distinguish values to 1 second in an easily-sortable format (numbers). The code to handle time of day is a bit tricky. Maybe you do not need that part. Here is the code I use.

# Converting date/time info to Unix time code

use Time::Local;

# timelocal() returns a Unix time code number
# Function timelocal() takes a 6-element list, the same as the first
# six arguments of the localtime function.  If you have
#   $timecode = timelocal @list;
# then mday = list[3] = 1..31
#      mon = list[4] = 0..11
#      yr = list[5] = year-1900

# Assume you have "hr:min:sec am/pm" as variables
# $arghr, $argmin, $argsec, $ampm      If the time-of-day
# does not matter, I usually set them as "12:1:1 am",
# (just after noon) to avoid being near a day changeover.
$arghr = $1;
$argmin = $2;
$argsec = $3;
$ampm = $4;

# Assume you have "day,mon,yr" as variables
#   $argday, $monname, $argyr
#   "day" = 1 .. 31
#   "mon" = Jan .. Dec
#   and 2-digit (21st century) year
$argday = $1;
$monname = ucfirst $2;
$argyr = $3;

# Given the above seven arguments, the following code
#  will produce the corresponding Unix (Perl) timecode value

%monhash =
( "Jan" =>1, "Feb" =>2, "Mar" =>3, "Apr" =>4, "May" =>5, "Jun" =>6,
  "Jul" =>7, "Aug" =>8, "Sep" =>9, "Oct" =>10, "Nov" =>11, "Dec" =>12 
+);

$hrmin = 0;
$hrmax = 23;
if ( $ampm ne "" )
{
  $hrmin = 1;
  $hrmax = 12;
  $addhrs = 0;
  if ( $ampm =~ /^p/ )
  {
    $addhrs = 12;
  }
}

if ( $arghr < $hrmin or $arghr > $hrmax )
{
  die "Hours portion of date argument '$arghr' out of range.\n";
}

if ( $ampm ne "" )
{
  if ( $arghr == 12 )
  {
    $arghr = 0;
  }
  $arghr += $addhrs;
}

if ( $argmin < 0 or $argmin > 59 )
{
  die "Minutes portion of date argument '$argmin' out of range.\n";
}

if ( $argsec < 0 or $argsec > 59 )
{
  die "Seconds portion of date argument '$argsec' out of range.\n";
}
print "The time arg is $arghr:$argmin:$argsec\n";

if ( not defined $monhash{ $monname } )
{
  die "Could not parse month portion '$monname' of date argument.\n";
}
$argmon = $monhash{ $monname };
$argyear = 1900 + $argyr;

$argtime = timelocal( $argsec, $argmin, $arghr,
             $argday, $argmon, $argyear - 1900 );
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