I have not kept track of my time, although now I wish I had. I think a running tally of hours worked and earnings per month would give a nice snapshot of hourly earnings over time. However, it would take some time for the data to be meaningful.
The more data, the more meaningful or accurate the rate would be. For example, this month I have already exceeded the payout level but have only put a few hours into one published hub, so I have a high hourly rate this month. Next month I may publish more but my earnings probably won't be much higher so my hourly rate will be lower. But the more months of data I have compiled together, the more accurate the hourly rate will be. At least I will have an idea if I am earning 10 cents an hour or $10 an hour.
So I think it's possible to estimate an hourly rate for an entire body of hubs, but not how much each specific hub earns for the hours put into that specific hub.