`@progress/kendo-intl` incorrectly formats timezone offsets whose minute component is non-zero.

For example, a JavaScript `Date` with the historical Warsaw offset `UTC+01:24` is formatted as `+01:04` instead of `+01:24`.

This affects all tested `Z`, `X`, and `x` timezone format variants.

Environment

- `@progress/kendo-angular-intl`: `24.2.0`
- `@progress/kendo-intl`: `3.2.1`

- Browser/Node timezone: `Europe/Warsaw`
- Operating system: Windows
- Format: `yyyy-MM-ddTHH:mm:ssZZZZZ`

The same formatting implementation appears in `@progress/kendo-intl` versions `3.1.2` and `3.2.1`.

Reproduction

const { formatDate } = require('@progress/kendo-intl');

process.env.TZ = 'Europe/Warsaw';

const date = new Date(1900, 0, 1, 16, 0, 0);

console.log(date.toString());
console.log(date.getTimezoneOffset());
console.log(formatDate(date, 'yyyy-MM-ddTHH:mm:ssZZZZZ'));

Actual Result

Mon Jan 01 1900 16:00:00 GMT+0124
-84
1900-01-01T16:00:00+01:04

Expected Result

1900-01-01T16:00:00+01:24

Date#getTimezoneOffset() returns -84, meaning the local timezone is 84 minutes ahead of UTC:

84 minutes = 1 hour 24 minutes

Other Examples

The issue is not limited to positive offsets:

UTC is also formatted differently depending on the token, but that behavior may be intentional:

Tested Format Specifiers

All applicable format variants use the same incorrect minute calculation:

Z      -> +0104
ZZ     -> +0104
ZZZ    -> +0104
ZZZZ   -> GMT+01:04
ZZZZZ  -> +01:04

X      -> +0104
XX     -> +0104
XXX    -> +01:04
XXXX   -> +0104
XXXXX  -> +01:04

x      -> +0104
xxx    -> +01:04
xxxxx  -> +01:04

Changing from ZZZZZ to XXXXX or XXX therefore does not resolve the problem.

Suspected Root Cause

The current formatter appears to perform approximately this calculation:

const offset = date.getTimezoneOffset() / 60;
const hoursMinutes = Math.abs(offset).toString().split('.');
const minutes = hoursMinutes[1] || 0;

For an 84-minute offset:

84 / 60 = 1.4

The decimal portion "4" is then treated as four minutes and padded to "04".

However, the fractional part represents a fraction of an hour:

0.4 hours * 60 = 24 minutes

Likewise, for 210 minutes:

210 / 60 = 3.5

The formatter produces 03:05, although 0.5 hours is 30 minutes.

Suggested Fix

Timezone offsets should remain integer minute values throughout formatting:

function formatTimeZone(date, info, options) {
    const totalMinutes = date.getTimezoneOffset();
    const absoluteMinutes = Math.abs(totalMinutes);
    const hours = Math.floor(absoluteMinutes / 60);
    const minutes = absoluteMinutes % 60;
    const sign = totalMinutes <= 0 ? '+' : '-';

    // Continue applying shortHours, separator, optionalMinutes,
    // localizedName and zZeroOffset options using hours and minutes.
}

The important calculations are:

const hours = Math.floor(Math.abs(offsetMinutes) / 60);
const minutes = Math.abs(offsetMinutes) % 60;

Converting the offset to a decimal hour and splitting its string representation is not reliable.

Suggested Regression Tests

it('formats a positive timezone offset with minutes', () => {
    const date = new Date(2024, 5, 25, 12, 7, 5);
    vi.spyOn(date, 'getTimezoneOffset').mockReturnValue(-84);

    expect(formatDate(date, 'yyyy-MM-ddTHH:mm:ssZZZZZ'))
        .toBe('2024-06-25T12:07:05+01:24');
});

it('formats a negative timezone offset with minutes', () => {
    const date = new Date(2024, 5, 25, 12, 7, 5);
    vi.spyOn(date, 'getTimezoneOffset').mockReturnValue(210);

    expect(formatDate(date, 'yyyy-MM-ddTHH:mm:ssZZZZZ'))
        .toBe('2024-06-25T12:07:05-03:30');
});

Other useful cases include:

-345 -> +05:45
-330 -> +05:30
210 -> -03:30
0 -> Z or +00:00, depending on the selected token

Impact

This can corrupt serialized date-time values when they are passed to systems that honor the emitted offset, including .NET DateTimeOffset.

Example:

Intended: 1900-01-01T16:00:00+01:24
Emitted:  1900-01-01T16:00:00+01:04

These values represent instants 20 minutes apart.

The issue affects:

• Historical dates from regions that previously used local mean time.
• Current timezones with half-hour or quarter-hour offsets.
• Any test or custom Date implementation returning a non-whole-hour offset.

Examples of modern fractional offsets include UTC+05:30, UTC+05:45, UTC+09:30, and UTC-03:30.

Additional Context

We initially encountered this with Europe/Warsaw and 1900-01-01. The JavaScript runtime correctly reports Warsaw's historical offset as UTC+01:24. The incorrect UTC+01:04 value is introduced only during Kendo formatting.

We have implemented a temporary application-level workaround that formats the date portion with Kendo and calculates the timezone offset directly from integer minutes.

StackBlitz