Finder Alters Time Of Calendar Events During Sync

Calendars are On My Mac (MBP, Sonoma 14.1.2) and On My Phone (iPhn 12, iOS 17.1.2), ie not using iCloud.


When I use Finder to sync the device, All-Day Events as appearing on the iPhone have one day added before the actual day as appearing on the MBP.


For example, an All-Day Event on Mon 1 Jan on the MBP will show as a two day event from Sun 31 Dec to Mon 1 Jan on the iPhn. A two day event on MBP shows as a three day event on iPhn.


When I check the box Replace Calendars During The Next Sync, events remain correct on the MBP but the syncing process modifies the events on the iPhn. If I don't check the box, ie an ordinary (two way) sync, events are modified on both. Luckily I export all Calendars to a drive before each sync so I'm able to delete corrupted calendars and import the genuine calendars back to the MBP but I can't get genuine all-day events on the iPhn.


Even if I delete all Calendars on the iPhn and sync which creates new calendars on the iPhn, they're still corrupt.


Appreciate any advice from anyone experiencing the same... and know how to resolve. Thank you, Steve H.

MacBook Pro (2017 – 2020)

Posted on Dec 7, 2023 08:49 AM

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4 replies

Dec 27, 2023 10:59 AM in response to Land4Sale

Yes, an all-day event has a particular time allocated. It's from midnight to midnight in the time zone in which it was created. The checkbox All-day event hides this detail.


Here's an experiment I made.

  • I activated time zone support on my computer.
  • I added another time zone in the drop-down menu at the top.
  • I created a normal one-hour event in a time zone different than the one displayed in the drop-down menu, then set it to all-day. Immediately the event was spread over the two columns because the starting time was moved to 11 PM on the previous day. But being an all-day event it was now considered all-day for both days.
  • I deactivated time zone support but the new duration was already "baked-in" so the duration stayed over two days.


My point is that time zones matter even if Calendar doesn't use them at the moment. Check both your phone and your computer to make sure they are set to the same time zone.


Time zones can be found at:

MacOS: System settings / General / Date and time

iOS: Settings / General / Date and time (switch automatic off for a moment to see the hidden time zone)

and Settings / Calendar / Time zone override (switch on for a moment to see the hidden time zone)

Jan 24, 2024 02:05 AM in response to Recycleur

Thank you and apologies for delayed reply (Christmas/New Year summer holidays over, back to the grindstone now).


I think you're onto something and I get it that time zones matter and if my two devices have different settings then during the sync process an Event can be modified on one device according to its settings. Do you think my Settings could be conflicting? Here they are:


  1. macOS / Calendar / Settings / Advanced > Turn on time zone support (off).
  2. macOS / Sys Settings / General / Date & Time > Set time and date automatically (on); Set time zone automatically using current location (on); Closest city (Pxxx).
  3. iOS / Settings / Calendar > Time Zone Override (on); Time Zone (Pxxx).
  4. iOS / Settings / General / Date & Time > Set automatically (on); This time zone cannot be set manually due to device restrictions.


I chatted to another staff member who receives invitations to the same Events as I do. She has the same problem although it manifests from a different path. I receive Calendar invites by Mail on my MBP only and use Finder to sync its Calendar with my iPhn. Like me, my work colleague does not have Cloud Calendars, she has them On My Mac and On My Phone but she has Mail active on both so clicking an invitation in Mail on her Mac creates the all-day Event correctly and clicking the invitation in Mail on her Phone creates an all-day event over two days; the correct day of the Event and the day preceding it.



Dec 8, 2023 06:30 AM in response to Land4Sale

When you say that "an All-Day Event on Mon 1 Jan on the MBP will show as a two day event from Sun 31 Dec to Mon 1 Jan", is it from 0:00 on 31 Dec to 0:00 on 2 Jan (i.e. duration of 48 hours), or is it more likely from 23:00 on Dec 31st to 23:00 on 1 Jan (i.e. still a duration of 24 hours)?


In the latter case it looks like your two devices are set to different time zones.

Dec 27, 2023 08:47 AM in response to Recycleur

Hi and thank you for replying. I appreciate your time.


An all-day event doesn’t have any particular time allocated. On the iPhn it appears in the grey band above the timed events and on the MBP it appears above the bold grey line above the timed events, in both cases scrolling up or down through timed events never changes the position of all-day events, they sit at the top so I’m unable to answer your question; are they from 0:00 to 0:00 etc.


I’ve attached screenshots of a MBP all-day event and the same event synced to the iPhn appearing over two days (hopefully Apple won't delete the attachments for reasons of privacy).


‘Turn on time zone support’ is not checked under the Advanced tab of MBP Calendar Settings.


‘Time zone override’ is switched on under iPhn Calendar Settings.


I can’t imagine that time zone support would affect all-day events.





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Finder Alters Time Of Calendar Events During Sync

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