What do you want to do if the pattern doesn't match?
If you don't care and just want to extract anything almost looking like a date:

$_="2003 % 05 % 1720:55:23";
s/\D+//g;
($y, $m, $d, $H, $M, $S)=unpack("a4a2a2a2a2a2", $_);
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If you want to take care:

$_="2003 % 05 % 1720:55:23";
    warn "wrong Date"
unless ($y, $m, $d, $H, $M, $S)=~ /(\d{4})\s+%\s+([01]\d)\s+%\s+([0-3]
+\d)([0-2]\d):([0-5]\d):([0-5]\d)/;
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