lol, it's just a little big with how it calculates when it runs out. fixable maybe but not really a problem
This has been a thing for over a year. It is simply to give you time to renew on the day/next day if you do not want to be seen without your supporter status
If it is auto-renewing then you do not need to worry about it - and if you want to buy it again you just go to the supporter tab where you bought it before - or buy another in game and put it in your vault for IcC/Max.