HI monks

I found the s/// doesn't work after replace once. look at below code:

use strict;
use warnings;

use DateTime;
use DateTime::Set;
use DateTime::Format::Natural;
use DateTime::Format::Oracle;

$ENV{'NLS_DATE_FORMAT'} = 'DD.MM.YYYY HH24:MI';

my $step = 1; # one day one jump
my $dt_from = DateTime->new(
    year       => 2017,
    month      => 10,
    day        => 16,
    hour       => 16,
    time_zone  => 'Asia/Taipei',
);
my $dt_to = DateTime->new(
    year       => 2017,
    month      => 10,
    day        => 17,
    hour       => 16,
    time_zone  => 'Asia/Taipei',
);
my $dt_next = $dt_from->clone->add(hours => $step);
$dt_next = $dt_to->clone if $dt_next > $dt_to;
my $indivparam_string = 'AutoE=1~AutoS=A~AutoT=1~TFrom=29.12.2017 06:4
+0:30.000 SDT Greenwich Standard Time~TTill=29.12.2017 16:00:00.000 SD
+T Greenwich Standard Time~PLSType=0~GroupID=5922~ChkGrp=1~JobDefRegis
+terSets=~';

while( $dt_next <= $dt_to){
my $string_from = DateTime::Format::Oracle->format_datetime($dt_from);
my $string_next = DateTime::Format::Oracle->format_datetime($dt_next);

print " from $string_from to $string_next \n";
print "old indiv string is $indivparam_string !!\n";
###########################################just for some case, you hav
+e to modify conn string directly#####################
$indivparam_string =~ s/From=\K\d\d\.\d\d\.\d{4}\s\d\d:\d\d:\d\d/$stri
+ng_from/;
$indivparam_string =~ s/Till=\K\d\d\.\d\d\.\d{4}\s\d\d:\d\d:\d\d/$stri
+ng_next/;

print "new indiv string is $indivparam_string !!\n";
    last if $dt_next == $dt_to;
    $dt_from = $dt_next->clone;
    $dt_next->add(hours => 1);
    $dt_next=$dt_to if $dt_next->clone->add(hours => 1) > $dt_to;
}

#output  
 from 17.10.2017 07:00 to 17.10.2017 08:00

old indiv string is AutoE=1~AutoS=A~AutoT=1~TFrom=16.10.2017 08:00.000
+ SDT Greenwich Standard Time~TTill=16.10.2017 09:00.000 SDT Greenwich
+ Standard Time~PLSType=0~GroupID=5922~ChkGrp=1~JobDefRegisterSets=~ !
+!
new indiv string is AutoE=1~AutoS=A~AutoT=1~TFrom=16.10.2017 08:00.000
+ SDT Greenwich Standard Time~TTill=16.10.2017 09:00.000 SDT Greenwich
+ Standard Time~PLSType=0~GroupID=5922~ChkGrp=1~JobDefRegisterSets=~ !
+!
[download]

But when I put the initial string in while loop, It works fine

use strict;
use warnings;

use DateTime;
use DateTime::Set;
use DateTime::Format::Natural;
use DateTime::Format::Oracle;

$ENV{'NLS_DATE_FORMAT'} = 'DD.MM.YYYY HH24:MI';

my $step = 1; # one day one jump
my $dt_from = DateTime->new(
    year       => 2017,
    month      => 10,
    day        => 16,
    hour       => 16,
    time_zone  => 'Asia/Taipei',
);
my $dt_to = DateTime->new(
    year       => 2017,
    month      => 10,
    day        => 17,
    hour       => 16,
    time_zone  => 'Asia/Taipei',
);
my $dt_next = $dt_from->clone->add(hours => $step);
$dt_next = $dt_to->clone if $dt_next > $dt_to;

while( $dt_next <= $dt_to){
my $string_from = DateTime::Format::Oracle->format_datetime($dt_from);
my $string_next = DateTime::Format::Oracle->format_datetime($dt_next);

print " from $string_from to $string_next \n";
my $indivparam_string = 'AutoE=1~AutoS=A~AutoT=1~TFrom=29.12.2017 06:4
+0:30.000 SDT Greenwich Standard Time~TTill=29.12.2017 16:00:00.000 SD
+T Greenwich Standard Time~PLSType=0~GroupID=5922~ChkGrp=1~JobDefRegis
+terSets=~';
print "old indiv string is $indivparam_string !!\n";
###########################################just for some case, you hav
+e to modify conn string directly#####################
$indivparam_string =~ s/From=\K\d\d\.\d\d\.\d{4}\s\d\d:\d\d:\d\d/$stri
+ng_from/;
$indivparam_string =~ s/Till=\K\d\d\.\d\d\.\d{4}\s\d\d:\d\d:\d\d/$stri
+ng_next/;

print "new indiv string is $indivparam_string !!\n";
    last if $dt_next == $dt_to;
    $dt_from = $dt_next->clone;
    $dt_next->add(hours => 1);
    $dt_next=$dt_to if $dt_next->clone->add(hours => 1) > $dt_to;
}
[download]

Please help me! Thanks in advance.