All the "nice methods or modules" run server side. Unless you know the client's time zone you are pretty much stuffed.

For a site where a log in is required you can ask for, and store, the user's time zone.

If you are a Javascript junkie then take a look at http://www.willmaster.com/possibilities/archives/wmp19990831001.shtml for a technique for determining a client's time zone.

www.maxmind.com/app/geoip_country

use strict;
use warnings;

use Geo::IP;
use DateTime;
use DateTime::TimeZone;

my $gi = Geo::IP->new(GEOIP_STANDARD);
my $country_code = $gi->country_code_by_addr('24.24.24.24');
print qq{Country:\t$country_code};

my $dt = DateTime->now;
foreach my $tz (DateTime::TimeZone->names_in_country($country_code)) {
  $dt->set_time_zone( $tz );
  print $tz . qq{\t} . $dt->hms();
}
__END__
$ perl -l 630749.pl
Country:        US
America/New_York        04:19:57
America/Detroit 04:19:57
America/Kentucky/Louisville     04:19:57
America/Kentucky/Monticello     04:19:57
America/Indiana/Indianapolis    04:19:57
America/Indiana/Knox    03:19:57
America/Indiana/Winamac 04:19:57
America/Indiana/Marengo 04:19:57
America/Indiana/Vevay   04:19:57
America/Chicago 03:19:57
America/Indiana/Vincennes       03:19:57
America/Indiana/Petersburg      03:19:57
America/Menominee       03:19:57
America/North_Dakota/Center     03:19:57
America/North_Dakota/New_Salem  03:19:57
America/Denver  02:19:57
America/Boise   02:19:57
America/Shiprock        02:19:57
America/Phoenix 01:19:57
America/Los_Angeles     01:19:57
America/Anchorage       00:19:57
America/Juneau  00:19:57
America/Yakutat 00:19:57
America/Nome    00:19:57
America/Adak    23:19:57
Pacific/Honolulu        22:19:57
[download]

You can get it with JavaScript and pass it to the server in a number of ways if that's what you want.

Just off the top of my head, you could set a cookie with JavaScript when a page loads, and read it back in your cgi script. You could do it with Ajax, using an XMLHTTPRequest which talks to a script on your server in the background. You could hack a redirect so that foo.html redirects to bar.html?localtime=<their localtime>.

All of those are dependent on their having the right browser and JavaScript turned on, etc.

How about getting client IP (which can be done), converting that to approximate geographical location, and from there to some approximation of time zone. At least one can figure out whether to say "good evening" or "good morning", based on this crude idea.

You could do that, but it's important to understand that it's a heuristic and not a real concrete method.

Another heuristic might be to look at the language preference information you get from the browser. You can guess that "en-US" is probably one of four time zones.

Still another would be a wild guess based on the server's local time. You can guess that most of your hits at any time of day come from time zones that are in "waking hours" at that time (i.e., the Australians are active at a different time than the Americans).

Quite a few sites I've been to (including this one) ask me my time zone as part of my user preferences. This is evidence enough for me that there isn't a good and easy solution to this problem.

This does not “record” the user’s time and, like others have said, it’s not possible to get the localtime from the user perfectly b/c you rely upon the user’s stuff being set right. If location specific display is your only goal then this is a nice trick, needs JS, to keep times neutered in the DB and let the clientside display what it believes to be the correct local version: Perl + JavaScript to display "correct" local times.