I would recommend setting up a Google Sheet with Google Analytics Add-on. Create report for all of the web properties and schedule reporting. Then you can create a new sheet called "Summary" that pulls all the data from the new sheets.
If you are looking for the date instead of timestamp of peak active users, it's fairly simple. Go to Audience > Overview > Update date range to maximum > Find peak in chart.
Try also this: Go to Query Explorer (ga-dev-tools.appspot.com/query-explorer)
Check out my settings:
metrics = ga:users
dimensions = ga:dateHourMinute
sort = -ga:users (...