I did see for the QueryHistoryProperty service that when selected in the Mashup design view, you see the oldestFirst property,
I also discovered that the Time Series Chart behaves differently than a Label Chart and it puts older values to the left in the chart and newer to the right.
This is more what I was expecting and so I just switched to Time Series Chart in my Mashup for displaying streamed Temperature and Humidity data.
I wish the Query Filter could allow relative queries such that I want the start of the data displayed to be the most recent midnight value rather than a specific midnight timestamp. The query syntax seems to be relative but the limits are made concrete once the query filter is saved.