First of all you are assigning to $time once, so even if the format will work you'll end with the same time at each print: you must call it at each iteration directly or with a sub.

Second I do not find %a to be valid in the format description, see the following code:

use strict;
use warnings;
use POSIX q(strftime);

my @abc = ("a", "b", "c", "d", "e");

foreach (@abc) { print '[',(strftime '%Y-%m-%d-%H-%M-%S', localtime())
+.
                       "]\t$_\n"; sleep 1;}


#output
[2017-06-07-11-19-36]   a
[2017-06-07-11-19-37]   b
[2017-06-07-11-19-38]   c
[2017-06-07-11-19-39]   d
[2017-06-07-11-19-40]   e
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L*