In Thunderbird calendar, on 27th Oct 2024, entries added are displayed one hour ahead of where they should be. If the entry is edited, the times are correct, and they show correctly in another calendar app (Calendar on my iPhone). The issue does not occur for events on the day before or the day after, and is the same for a newly added event as for an existing one. See screen shots. You can see my test event displayed at 11:00 - 12:00 but on editing it is actually 10:00 - 11:00 - the latter is correct. 27th Oct is the day that DST ends in the UK (at 0200) in 2024, but the events are several hours after that. Nick.