I don’t believe that there is any guarantee that the Encounter effective time is the same as the facility arrival and departure times. It may be that the Encounter start and end times are the Admission and Discharge times but again that does not mean they are equal to the facility arrival and departure times. You can arrive at a facility before being admitted and get up and leave before being officially discharged. If you need facility departure or arrival time then it would need to be included in an optional Facility template. Based on the way the measure is written then that has the potential for affecting the calculation if the Encounter start and end times are wildly off from the facility arrival and departure times. But the calculation is still based off the facility arrival and departure times and are included in the Cat I documents in the Facility template. [1/30/2015] The QRDA-I template for “Encounter, Performed” supports two different datetimes: 1) For Admission and Discharge datetime, they are mapped to “encounter/effectiveTime/low” and “encounter/effectiveTime/high”. 2) For the Facility Location Arrival Datetime and the Facility Location Departure Datetime attributes of “Encounter, Performed”, they are mapped to “encounter/participant/time/low” and “encounter/participant/time/high”. In the “Encounter Performed” QRDA template, it contains the following conformance statement “MAY contain zero or more [0..*] Facility Location (templateId:2.16.840.1.113883.10.20.24.3.100) (CONF:13025).”. Participant/time is specified in the Facility Location template.