After recurring rules, time zones cause the most interoperability troubles. The good news is that most of the issues are due to the recurring rules – which have been removed from iCAL-Basic. Removing time zones from ICAL-Basic will allow better approaches to be applied when ICAL-Basic is extended.
ICAL-Basic will supports both local times and single instances specified in Coordinated Universal Time (UTC). The two proposed formats are as follows:
FORM #1: DATE WITH LOCAL TIME
The date with local time form is a date-time value that does not contain the UTC designator. For example, the following represents January 18, 1998, at 11 PM: DTSTART:19980118T230000.
These local date-time values are said to be "floating" and are not bound to any time zone in particular. They are used to represent the same hour, minute, and second value regardless of which time zone is currently being observed.
FORM #2: DATE WITH UTC TIME
The date with UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC designator, appended to the time value. For example, the following represents January 19, 1998, at 0700 UTC: DTSTART:19980119T070000Z
This format requires that your calendar application (desktop, web, PDA, cell phone, etc.) will need to know your local time zone and perform the calculations from UTC.