I check at the beginning of each month to make sure my titles are up where they’re supposed to be and to record the sales.
It would take more time if I had more books. This is the summary over time; one title dates back to 2011 and the other was published this year. I hear a lot of people wanting to sell on Amazon only. In my case, that would mean cutting 2/3 of my revenue.
I also have a spreadsheet that tracks each title month-by-month, with a different tab for each year.