COMMONS13 — Could a "date period" be defined even without knowing the exact dates?

The specificaton of DatePeriod states: "A date period is unknown if either the start date or the end date has no value. If a date period
is unknown, then the duration should either be omitted or unknown (have no value)."
What about the situation in which the period is known but the dates are not yet known? For example, as I write this we know that OMG's Q2 meeting will be over 5 calendar days, but it may be June 12-16 or June 19-23. There could be a date period associated to such an entity (meeting) that don't have a start date or end date, but have a known duration, which should be recorded. "Duration" is not necessariiy a good substitute because it is not limited to a date range.