It's been 2 months since I last updated it, so bi-monthly wouldn't be a bad idea, but I'd keep it up for the monthly report because it makes more sense that way.
IMO, it's still better to update it every 2 months than not to do it at all. LOL
For people who care about forum stats, merit and any activity on local board then I think they probably already know how to calculate it so far. Merit Dashboard and Ninjastic.space are two really helpful tools, so it probably wouldn't be a problem if the OP only had time to update them every 2 months.
But if someone takes the initiative to do so and updates it monthly, then I think the OP would welcome it. I don't think he'll be mad about it, but surely someone might need permission to hijack the thread. LOL