#! /usr/bin/perl
use strict;
use warnings;
use List::Util qw( min );

my %hash = (
    't1' => [0.5, 0.8],
    't2' => [0.6, 0.9],
    't5' => [0.4, 0.2],
);

my $min = min map { $hash{$_}->[0] } keys %hash;

print "Min: $min\n";