For what I see from the discution it seems to be more a practical decision to not use real time resources and techniques for much higher times. So 1 day for example would be a waste of development time to try to use real time, you could use alerts and background jobs to fix issues. But when you reach shorter and shorter timeframes and bad things can happen a real time approach starts to make more sense.

Now, some parent comment mentioned RTOS. Maybe for a real time OS there would be a practical hard upper bound. But for real time systems in general this upper bound would be totally domain specific.