use strict;
use warnings;
use File::ReadBackwards;

my $log   = ...;
my $fh    = File::ReadBackwards->new($log) or die "Cannot read '$log': $!";
my $found = 0;

while (my $line = $fh->readline)
{
    if ($line =~ /.../)     # Identify a JVM line and capture the timestamp
    {
        ...;                # Re-format the timestamp and export it
        $found = 1;
        last;
    }
}

warn "No log entry found\n" unless $found;