You can use both a buffer size and a timespan to buffer values. The buffered values are emitted if either the buffer is full or if the time slot ends and a new one starts. Note that, as of the writting of this guide, the [marble diagram for this operator](https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/buffer6.png) is misleading, as it shows that a timespan resets if a buffer is emitted because it is full.