Left of the "." is the number of seconds since Jan 1st, 1900 UTC.

Right of the "." is the number of 1/(2**32)th of seconds.

use Time::HiRes qw( time );

# Number of secs between 1900/01/01 UTC and 1970/01/01 UTC.
my $ntp_epoch_diff = 2208988800;

my $time = time();
my $ntp_ts = sprintf('%08X.%08X',
    int($time) + $ntp_epoch_diff,
    ($time - int($time)) * (2**32),
);
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(I don't know if the number of secs is correct.)