You can find the parameter listed, together with a short documentation, in the sample adapters.xml file of the StockListDemo Remote Adapter example in LS distribution package, in
DOCS-SDKs\sdk_adapter_dotnet\examples\Remote_StockListD emo_Adapters\Deployment\Deployment_LS\StockList_so ckets

So, you can add the line; the value is in milliseconds.
The timeout should only account for roundtrip delays in the Proxy Adapter / Remote Adapter communication;
in fact, we suggest that the Subscribe implementation should not be blocking.

The default timeout is 10000. A shorter timeout may cause more slow subscriptions to be refused. A very high timeout has a side effect on memory usage with a large number of subscriptions, which will be fixed only in the next release.