Added information on timestamp format for time comparison operators

Author: Olesia

src/engage/audiences/index.md

@@ -42,6 +42,11 @@ You can also use computed traits in an Audience definition. For example, you can
 > info ""
 > Engage supports nested traits, but the Audience builder doesn’t support accessing objects nested in arrays. When you send arrays of objects, they are flattened into strings. As a result, the same conditions that work on strings will work on the array. Within the builder, you can only use string operations like `contains` and `does not contain` to look for individual characters or a set of characters in the flattened array.
 
+### Time Comparision
+
+You can use various time comparison operators in your Audience definition. Such operators are: before date, after date, within last, within next, before last, after next. Only ISO timestamps can be used with these operators.
+If the timestamp is not a valid ISO timestamp (for example, a trailing 'Z' is missing), it will not be processed by Real-time compute. See [Real-time compute compared to batch](docs/engage/audiences/#real-time-compute-compared-to-batch)
+
 ### Funnel Audiences
 
 Funnel audiences allow you to specify strict ordering between two events. This might be the case if you want an event to happen or not happen within a specific time window, as in the following example: