Laravel migration and seeder for importing timezones. it uses timezone_identifiers_list() php standard function and including name, offset and diff_from_gtm details for each timezone.

LaravelTimeZoneSeeder.php

<?php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateTimezonesTable extends Migration
{
    /**
     * Run the migrations.
     *
     * @return void
     */
    public function up()
    {
        Schema::create('timezones', function (Blueprint $table) {
            $table->id();
            $table->string('name');
            $table->string('offset');
            $table->string('diff_from_gtm');
        });
    }

    /**
     * Reverse the migrations.
     *
     * @return void
     */
    public function down()
    {
        Schema::dropIfExists('timezones');
    }
}

TimezoneMigration.php

<?php

namespace Database\Seeders;

use App\Models\Timezone;
use Illuminate\Database\Seeder;

class TimezoneSeeder extends Seeder
{
    /**
     * Run the database seeds.
     *
     * @return void
     */
    public function run()
    {
        $timestamp = time();
        foreach (timezone_identifiers_list() as $zone) {
            date_default_timezone_set($zone);
            $zones['name'] = $zone;
            $zones['offset'] = date('P', $timestamp);
            $zones['diff_from_gtm'] = 'UTC/GMT ' . date('P', $timestamp);

            Timezone::query()->insert($zones);
        }
    }
}