There's also strftime in core module POSIX, as mentioned in the docs for localtime. 
use POSIX qw( strftime );
my $time = 400_000_000;
print strftime("%y/%m/%d %H:%M\n", localtime($time));

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Update: Changed "%Y" to "%y" to match OP's format.

In reply to Re: seconds since the epoch by ikegami
in thread seconds since the epoch by my_nihilist

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