It will render until all pixels reach the 100 subdivs or the render time reaches the limit of 6 hours, whichever happens first.
You can set the max subdivs to some high value that can’t be reached for the specified time, f.e. 1000 which is 1 million samples for each pixel. This way it will stop on the time limit.
Of course, noise threshold of 0 disables the adaptive sampling and will waste a lot of time on areas that don’t need much sampling.