CSV files are two dimensional (lines of fields). Your data is also two dimensional. To parse your data as a CSV file, each hash element would need to be parsed as a line.

use strict;
use warnings;

use Data::Dumper qw( Dumper );
use Text::CSV_XS 0.74;  # eol bug fix.

my $csv = Text::CSV_XS->new({
   binary   => 1,
   sep_char => ':',
   eol      => ',',
});

while (<DATA>) {
   chomp;

   my %h;
   open(my $fh, '<', \$_) or die;
   while (my $row = $csv->getline($fh)) {
      $h{ $row->[0] } = $row->[1];
   }

   $csv->eof
      or $csv->error_diag();

   print(Dumper(\%h));
}

__DATA__
"evt":"Login","time":"now","msg":"Login success, welcome back!"
[download]

$VAR1 = {
          'msg' => 'Login success, welcome back!',
          'time' => 'now',
          'evt' => 'Login'
        };
[download]

One catch: eol doesn't work for anything but "\n" in 0.73, and 0.74 isn't out yet. (The bug has been fixed, but a release hasn't been created yet.)