Time Zone

I am storing values in db regarding following code but how i will mange it for each user.

<option value="-12">(GMT -12:00) International Dateline West</option>
                                    <option value="-11">(GMT -11:00) Midway Island, Samoa</option>
                                    <option value="-10">(GMT -10:00) Hawaii Island</option>
                                   ...