UniRx | Reactive Extensions for Unity | Reactive Programming library

I'm using the UniRx flavor of Reactive Extensions for the Unity3D game engine. Unity uses C#, so I guess it's similar to Rx.NET.

I need a more beautiful way of checking when several observable sequences complete.

In the example below, one of the sequences is dependent on the outcome of the first (since it needs an integer for processID).

The observables are both of type IObservable.

The problem: there is a stream of numeric values. Values are pushed in bursts so 100 values can come very close to each other (time-wise) say each 5-10 ms and then it possibly stops for a while, then can burst again.The idea is to show accumulated value (sum) of windows of at most length of 500 ms.

My first attempt was with Buffer(500ms) but this is causing constant pumping of events (every 500 ms) with the sum of 0 (as the accumulated buffer items os 0), it could be fixed with filtering by empty buffers but I would really like to avoid that entirely and only open the buffering after a value is actually pushed after a period of "silence".

Additional restrictions: the implementation is UniRx which does not contain all the Rx operators, notably Window (which I suspect could be useful in that case) so solution is limited to basic operators including Buffer.