To illustrate the effect noted in choroba's reply try the following:

use strict;
use warnings;

my $body_text="5 minutes left. Wait 6 minutes before nagging again.";

if ($body_text=~m/(\d{1,2})(?=\smins|\sminutes)/g) {
    print "1st try: " . $1 . "\n";
}

if ($body_text=~m/(\d{1,2})(?=\smins|\sminutes)/g) {
    print "2nd try: " . $1 . "\n";
}
[download]

Prints:

1st try: 5
2nd try: 6
[download]