Can I check the activity volume and duration on a specific day

You won't be able to do this using the built in viewer, however you can query the sql tables directly and then interrogate the results using your preferred method.

For example, I had a spike in activity on the 20th of Dec which made a disk fill a lot more than usual, but the purges meant I couldn't just check the messages as they had since been deleted. So I ran the following in the SQL option in the management portal:

SELECT *
FROM Ens_Activity_Data.Days
Where TimeSlot = '2020-12-20 00:00:00'

I then used the print option to export to CSV to then use a simple Pivot table to work through each Host name to see what had a dramatically higher number of messages to what I would usually expect. (I actually exported a few days worth of data to compare between days, but hopefully you're getting the idea)

You could always explore using Grafana to produce a nice visual representation of the data that you've surfaced using a method like this.