The above does it for you, but to answer your real questions: You can either use a regex or substr:

$stamp =~ /^.{3}(.*)/$1/;
$stamp = substr($stamp,3); #<---- this is much faster
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The : is done like your \ but just replace it with nothing.
the _20xx_ problem is: $stamp =~ /_\d{4}_//;
You can handle the \ space and colon with a single command: tr/\/ :/_/d

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