the issue is/ :, the leading zero in the time is also need to be removed.

So why not account for that? You could use a negative lookbehind as in this SSCCE:

use strict;
use warnings;

use Test::More tests => 1;

my $datetime = '01/08/2018 05:58';
my $want = '1/8/2018 5:58';

my $have = $datetime;
$have =~ s/(?<![:\d])0//g;
is ($have, $want);
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If you use <code> tags in your post your code will render better too.