Improved techniques are provided for processing streams of data. The duration of the time that an event is eligible for remaining in a time-based window can be variable for different events received via the same event stream. In certain embodiments, the duration of time that an input event spends in a time-based window is a function of one or more values of one or more attributes of the event. Since different events can have different one or more attribute values, the different events can spend different amounts of time in the time-based window for that event stream. The amount of time that an event spends in a time-based window can be controlled via the one or more attributes of the event.