How Can Recurring Events Be Managed Accurately Across Time Zones, Considering Daylight Saving Time?

Managing Repeating Dates with Daylight Savings Time in Mind

When storing recurring events across multiple time zones, it's crucial to consider the impact of Daylight Savings Time (DST). Storing date and time values solely in UTC may not accurately reflect local event times, particularly for future recurring events.

Recommended Approach

Instead of using UTC, consider storing the following information:

• Local time of the recurring event (e.g., "08:00")
• Time zone of the local time (e.g., "America/New_York")
• Recurrence pattern (e.g., daily, third Thursday of the month)
• Next immediate UTC equivalent date and time
• Optionally, a list of projected future UTC date and times

This approach allows for storing local event times effectively while also enabling the calculation of UTC equivalents for display purposes.

Alternative Approach (Using UTC as a Starting Point)

An alternative method involves converting a local time to UTC for storage and storing the time zone ID. At runtime, the original UTC time is converted back to local time, and local time is used to compute recurrences. However, this approach has potential drawbacks, including:

• Susceptibility to time zone updates that may alter the local time
• Difficulty managing floating times across different time zones
• Added complexity without substantial benefits

It's recommended to reserve this approach for scenarios where retrofitting time zone support into an existing UTC-only scheduler is necessary.

Conclusion

Storing recurring dates with DST in mind requires careful consideration. The proposed approach provides a robust method that accommodates the nuances of time zone transitions and recurrence patterns.

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