Yes, all-day events are usually TYPE=DATE and without a timezone. According to the RFC, if they are TYPE=DATE then they can not have a timezone.
The idea is that “all day” events happen on that calendar day, not at some time period of a day. If one wants a time-shifting “all day” event, you need to set the time, even if it covers all 24 hours.
I suppose what would be possible is to provide an option that could be passed into ICal.from_ics (or from_file) which would define a “apply this timezone to everything in this calendar”, and perhaps another one that would coerce all TYPE=DATE entries into DateTimes with a timezone … but that probably would not produce results that match what Office265 intends/expects.
If you feel that the dates should be parsed as datetimes, or you simply would like them to be 
, please open an issue on the ICal repo with a sample file (after removing any PII, of course) with a description of expected results and we can take it from there.
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