Setting dates and times
The rfc allows a number of forms for date and date time values.
This does not have a time component: from the RFC
The "VEVENT" is also the calendar component used to specify an anniversary or daily reminder within a calendar. These events have a DATE value type for the "DTSTART" property instead of the default data type of DATE-TIME. If such a "VEVENT" has a "DTEND" property, it MUST be specified as a DATE value also. The anniversary type of "VEVENT" can span more than one date (i.e, "DTEND" property value is set to a calendar date after the "DTSTART" property value).
An event with a DATE start does not take up time. Also as there is no timezone component it does not accurately flag the start and end of a day at any specific location.
An all-day event which does take up time should be flagged with a datetime start and end.
UTC date/time values have no timezone component. These values may be appropriate for export to devices which have no timezone support. They are displayed in the local (or currrent) timezone for convenience.
To set such a value, select the storeUTC checkbox when setting the time.
These are date/time values which have no timezone but are expressed in local time. These are approrpiate for events which take place at the same local time, for example, "13:00 - have lunch".
Date/time and timezone
These values have a timezone associated with them. An event can be specified with a different timezone for start and end, for example a flight from East coast USA to the UK.