Add new rule: "SHOULD select appropriate one of date or date-time format"

chapters/data-formats.adoc

@@ -124,6 +124,21 @@ issues with precision, e.g. whether to represent a timestamp as 1460062925,
 more effort to parse, avoid this ambiguity.
 
 
+[#255]
+== {SHOULD} select appropriate one of date or date-time format
+
+When choosing between `date` and `datetime` formats you should take into account the following:
+
+* `date` should be used for properties that are not time-sensitive or where precise timing is not required,
+for instance, document dates, birthdays, ETAs (estimated time of arrival).
+Normally date without time implies the time period from midnight to midnight in the local time zone.
+Since time zone information is absent in the property value, it must be documented and can be also provided
+as an additional context via other fields indicating location.
+* `datetime` should be used in all other cases to indicate instants/moments in time.
+This format requires the explicit time zone offset to be provided,
+which avoids misinterpretations and eliminates the need of an additional context to provide.
+
+
 [#127]
 == {SHOULD} use standard formats for time duration and interval properties