Hi. I've seen this queried in other places, but the answers only suggested software updates that predated mine.
When I create an all day event in my iphone (iOS 9.3.1) it shows up in my Outlook for Mac 2016 (15.19.1) across two days. It shows correctly on my phone but when I check the time zone in Outlook it appears as Coordinated Universal Time. I'm in London, which is an hour later than that and so the event appears as beginning at 23:00 the day before, yet sits across two later days.
For example, I've just created an all day event on Wed 13 Apr 2016. It shows correctly on my iphone. When I look at it on Outlook it sits across 13 and 14 Apr, but when I open it to edit it, it says that it runs from 12 April at 23:00 to 12 April at 23:00 in UTC. My time zone preferences on both my iphone and outlook calendars are set to London and I have time zone override set up on my iphone.
When I set up a timed event (ie beginning at 13:00 and ending an hour later) everything shows correctly. The problem only seems to be occurring for all day events. Help please!