Plant summary doesn't have a date, as it's just "NOW" so assumes you don't need it/already know it.
If you want latest live data with a timestamp then it's probably going to be this one from the Misc API:
https://www.givenergy.cloud/GivManage/invData/**$SerialNum**/**yyyy-MM-dd**?page=1&rows=1
Example Output:
{"total":174,"rows":[{"vpv2":"177.30","vpv1":"288.40","loadPower":"289.00","moduleVoltage":"53.40","importEnergyToday":"7.90","ppv2":"45.00","exportEnergyToday":"0.10","fac":"49.96","invImportEnergyToday":"6.40","invImportEnergyTotal":"1901.40","batPower":"31.00","ppv1":"78.00","ipv2":"0.20","ipv1":"0.20","pac":"-129.00","pacr":"0.00","meter2ActivePower":"-129.00","pacs":"0.00","pact":"0.00","invVoltage":"244.30","temperature":"25.80","batCurrent":"0.58","batPercent":"31.00","meter2PowerFactor":"10820.00","meter1ActivePower":"180.00","runtime":"8459.00","invFrequency":"49.94","vact":"5743.00","eacTotal":"7749.10","vacs":"0.00","eacToday":"4.70","vacr":"246.60","gridExportEnergyTotal":"3474.50","meter2ApparentPower":"483.00","batVoltage":"53.25","iacr":"1.20","ppv":"123.00","iact":"6273.90","iacs":"0.00","time":"2022-02-13
14:43:48","chgTemperature":"26.10","batTemperature":"10.00","gridImportEnergyTotal":"7067.80","status":"NORMAL"}]}
The "rows" bit set to 1 just returns the latest "row" of data. Picking a higher number just returns more of the history.
The only PITA is having to set the date variable all the time. I do this in powershell personally