I haven't found it to be exhausted in 40-50 minutes (20c), I've done 1+100 2 hour semi-stand
Maybe..... I did 1+150 in testing Tech Pan films and you will find no difference (densitometer) 1 h or 2 h semi-stand. But a higher dilution is quicker oxydized. 1+100 is then maybe on the edge. So 1+50 will then certainly work till two hours.
But on lower temperatures the process of oxydizing is also ran slower.