Timing Repeat have Length/Range of lengths, or (Start and/or end) limits which indicates either a duration for the length of the timing schedule, a range of possible length, or outer bounds for start and/or end limits of the timing schedule. Timing.repeat.duration indicates How long this thing happens for when it happens. If durationMax is present, this element indicates the lower bound of the allowed range of the duration. For some events the duration is part of the definition of the event (e.g. Intravenous (IV) infusions, where the duration is implicit in the specified quantity and rate). For others, it’s part of the timing specification (e.g. exercise). Some activities are not instantaneous and need to be maintained for a period of time.
Note, though, that some systems include timing details in something like ‘Dosage instructions’ which is wider than just Timing; those systems do not use the Timing data type. Other systems use a set of ‘common’ codes – including, but usually not limited to, widely understood acronyms such as “bis in die (BID)” which means in Latin, twice a day. If a Timing.code is provided, the code is understood to be a complete statement of whatever is specified in the structured timing data (except for Timing.repeat.bounds, which applies to the code), and either the code or the data may be used to interpret the Timing. A structured timing specification should be provided whenever possible, unless the code is BID, ter in die (TID) which in Latin means three times a day, quater in die (QID) which in Latin means four times a day, ante meridiem (AM) which in Latin means Before Midday or Post Meridiem (PM) which in Latin means After Midday, which have a ubiquitous meaning.
These codes shall be understood as having the formal meanings. Note that BID, etc. are defined as ‘at institutionally specified times’. For example, an institution may choose that BID is “always at 7am and 6pm”. If it is inappropriate for this choice to be made, the code BID should not be used. Instead, a distinct organization-specific code should be used in place of the HL7-defined BID code and/or a structured representation should be used (in this case, timeOfDay).