No timestamp on dailyTotals

[watersnake1]

I am trying to use the dailyTotals endpoint on https://api.thegraph.com/subgraphs/name/synthetixio-team/synthetix-exchanges. It works fine with a query like dailyTotals { exchangeUSDTally } but I do not understand how I am supposed to interpret this data, since there is no timestamp field that can be passed as a parameter or extracted from the endpoint. To which days do these totals correspond?