I don't think there's a built in method in Casper to do this. Maybe, perhaps the Events API? I don't know much about it, but it may be something to look at.
Outside of that, what I'd suggest doing is creating a new script to run as part of your imaging process that would write a date and timestamp into a local hidden file (or plist) on the Mac. You might need to have it run at first boot, but it may also work as part of the initial imaging process.
Second, create an Extension Attribute script that looks for that local hidden file and extracts the date and timestamp from it and populates the EA with that value.
Once all that's set up, you would be able to generate a report on the time that machines were imaged. Not sure if it would be practical to do a report on last x hours. Last x days, yes, but I don't know if there's anything in the JSS reporting that would allow you to look at hours increments for reporting purposes.
As for the second request, what do you mean exactly by software downloaded in the last x hours? From Self Service? Or just in general?
