> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hyperline.co/llms.txt
> Use this file to discover all available pages before exploring further.

# Dates & timezones

> Understand how Hyperline represents dates, datetimes, and timezones across the API: ISO 8601 formatting, UTC defaults, and billing-cycle conventions.

The Hyperline API handles all dates in UTC (Coordinated Universal Time). When sending dates to the API, you must convert your local timezone dates to UTC. Similarly, the API returns all dates in UTC.

## Working with customer timezones

When creating subscriptions for customers in specific timezones, you'll need to convert the desired local time to UTC before sending it to the API.

### Examples

For example, to create a subscription that starts at midnight (00:00) in Paris timezone (Europe/Paris), send the following UTC values:

```javascript theme={null}
// Example 1: January 1st, 2024 at 00:00 Paris time
// Paris is UTC+1 in winter, so we need to convert to UTC (23:00 previous day)
"2023-12-31T23:00:00Z"

// Example 2: July 1st, 2024 at 00:00 Paris time
// Paris is UTC+2 in summer (due to daylight saving), so we need to convert to UTC (22:00 previous day)
"2024-06-30T22:00:00Z"
```

Note that the `Z` suffix in the date string indicates that the timestamp is in UTC.

## Best practices

* Always use ISO 8601 format for dates
* Include the UTC indicator (`Z`) in your timestamps
* Consider daylight saving time when converting from local timezones
* Use a reliable date library (like `date-fns` or `luxon`) to handle timezone conversions


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