Mmm, unlimited is not completely correct. When starting parking outside the “Maximale Parkdauer” period you can maximally park till 10:00 in the next period. So depending on when you start parking the maxstay is something between 16 and 10 hours
Despite its name, unlimited means “until the next restriction applies”. Which can be actually unlimited if there is no such restriction, but is usually overridden via maxstay:conditional.
Others use maxstay=no to mean that, which I find to be an even worse value.