Hi Matty,
What's your local time zone setting in Windows 10? Also check the Outlook 2016 Time Zone setting in File > Options > Calendar > Time Zone.
I notice that this Internet Calendar is an Office 365 shared Calendar, please access this Office 365 mailbox in Outlook on the web, check the Time Zone setting for this mailbox in Settings > Options > General > Region and time zone.
In Outlook client, create a new appointment on this Calendar, check the time zone for this items. Also create another new appointment in the source shared calendar from the original mailbox in Outlook on the web (Office 365).
If the time zone is still shown incorrectly in all above scenarios, try to unsubscribe for this Calendar, remove caches in Outlook 2016, create a new Outlook profile and re-subscribe this Calendar in new profile to have a try.
Best Regards,
Winnie Liang
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