Traffic Monitor - Starting Day of Monthly Cycle

[Rowbby]

My ISP tracks my usage based on my billing cycle instead of the first of the month so I'm trying to change the traffic monitor to reflect that, but I'm having trouble getting it to apply the change correctly. I changed the date to the 26th yesterday and applied it, but after midnight, it's still tracking monthly usage as part of February when it should have switched to March. I tried rebooting the router (after midnight) to see if it would start the new month; It didn't. Do I need to enable "create/reset data files" to get the change applied correctly? I was trying to avoid doing that since I'd like to keep the stats I have if possible.

Thanks!

RT-N66U on 378.54_2