Can I get the browser time zone in ASP.NET or do I have to rely on JS operations to retrieve the information?

There is no “Accept-Timezone” header (or the like) – the HTTP standard does not contain any facility to allow the browser to automatically tell the server what time zone the user cares about.

The basic approach is to use a date and read the TZ info from it.

Since there’s no standard (cross-browser time zone naming functions – you have to resort to something like (yikes!):

function getTimezoneName() {
    tmSummer = new Date(Date.UTC(2005, 6, 30, 0, 0, 0, 0));
    so = -1 * tmSummer.getTimezoneOffset();
    tmWinter = new Date(Date.UTC(2005, 12, 30, 0, 0, 0, 0));
    wo = -1 * tmWinter.getTimezoneOffset();

    if (-660 == so && -660 == wo) return 'Pacific/Midway';
    if (-600 == so && -600 == wo) return 'Pacific/Tahiti';
    if (-570 == so && -570 == wo) return 'Pacific/Marquesas';
    if (-540 == so && -600 == wo) return 'America/Adak';
    if (-540 == so && -540 == wo) return 'Pacific/Gambier';
    if (-480 == so && -540 == wo) return 'US/Alaska';
    if (-480 == so && -480 == wo) return 'Pacific/Pitcairn';
    if (-420 == so && -480 == wo) return 'US/Pacific';
    if (-420 == so && -420 == wo) return 'US/Arizona';
    if (-360 == so && -420 == wo) return 'US/Mountain';
    if (-360 == so && -360 == wo) return 'America/Guatemala';
    if (-360 == so && -300 == wo) return 'Pacific/Easter';
    if (-300 == so && -360 == wo) return 'US/Central';
    if (-300 == so && -300 == wo) return 'America/Bogota';
    if (-240 == so && -300 == wo) return 'US/Eastern';
    if (-240 == so && -240 == wo) return 'America/Caracas';
    if (-240 == so && -180 == wo) return 'America/Santiago';
    if (-180 == so && -240 == wo) return 'Canada/Atlantic';
    if (-180 == so && -180 == wo) return 'America/Montevideo';
    if (-180 == so && -120 == wo) return 'America/Sao_Paulo';
    if (-150 == so && -210 == wo) return 'America/St_Johns';
    if (-120 == so && -180 == wo) return 'America/Godthab';
    if (-120 == so && -120 == wo) return 'America/Noronha';
    if (-60 == so && -60 == wo) return 'Atlantic/Cape_Verde';
    if (0 == so && -60 == wo) return 'Atlantic/Azores';
    if (0 == so && 0 == wo) return 'Africa/Casablanca';
    if (60 == so && 0 == wo) return 'Europe/London';
    if (60 == so && 60 == wo) return 'Africa/Algiers';
    if (60 == so && 120 == wo) return 'Africa/Windhoek';
    if (120 == so && 60 == wo) return 'Europe/Amsterdam';
    if (120 == so && 120 == wo) return 'Africa/Harare';
    if (180 == so && 120 == wo) return 'Europe/Athens';
    if (180 == so && 180 == wo) return 'Africa/Nairobi';
    if (240 == so && 180 == wo) return 'Europe/Moscow';
    if (240 == so && 240 == wo) return 'Asia/Dubai';
    if (270 == so && 210 == wo) return 'Asia/Tehran';
    if (270 == so && 270 == wo) return 'Asia/Kabul';
    if (300 == so && 240 == wo) return 'Asia/Baku';
    if (300 == so && 300 == wo) return 'Asia/Karachi';
    if (330 == so && 330 == wo) return 'Asia/Calcutta';
    if (345 == so && 345 == wo) return 'Asia/Katmandu';
    if (360 == so && 300 == wo) return 'Asia/Yekaterinburg';
    if (360 == so && 360 == wo) return 'Asia/Colombo';
    if (390 == so && 390 == wo) return 'Asia/Rangoon';
    if (420 == so && 360 == wo) return 'Asia/Almaty';
    if (420 == so && 420 == wo) return 'Asia/Bangkok';
    if (480 == so && 420 == wo) return 'Asia/Krasnoyarsk';
    if (480 == so && 480 == wo) return 'Australia/Perth';
    if (540 == so && 480 == wo) return 'Asia/Irkutsk';
    if (540 == so && 540 == wo) return 'Asia/Tokyo';
    if (570 == so && 570 == wo) return 'Australia/Darwin';
    if (570 == so && 630 == wo) return 'Australia/Adelaide';
    if (600 == so && 540 == wo) return 'Asia/Yakutsk';
    if (600 == so && 600 == wo) return 'Australia/Brisbane';
    if (600 == so && 660 == wo) return 'Australia/Sydney';
    if (630 == so && 660 == wo) return 'Australia/Lord_Howe';
    if (660 == so && 600 == wo) return 'Asia/Vladivostok';
    if (660 == so && 660 == wo) return 'Pacific/Guadalcanal';
    if (690 == so && 690 == wo) return 'Pacific/Norfolk';
    if (720 == so && 660 == wo) return 'Asia/Magadan';
    if (720 == so && 720 == wo) return 'Pacific/Fiji';
    if (720 == so && 780 == wo) return 'Pacific/Auckland';
    if (765 == so && 825 == wo) return 'Pacific/Chatham';
    if (780 == so && 780 == wo) return 'Pacific/Enderbury'
    if (840 == so && 840 == wo) return 'Pacific/Kiritimati';
    return 'US/Pacific';
}