Although I'm not a big fan of "minimum efforts" when it comes to organ practice, I can understand people who are asking this question. Not too many people can devote 3-4 hours a day for practicing organ music. Only full time concert organists can do that and even they have to face multiple other tasks in their day.
So it's only natural for a person who only has, say total of 60 minutes a day for organ practice to wonder if it's reasonable to expect results from a short period of practicing technical exercises.
What I had found through my personal practice is that it takes about 10 minutes of playing just to warm up my fingers. So anything less than that will hardly produce any effect in the long run.
But if you could spend about 20 minutes a day playing scales, arpeggios, or Hanon exercises after a period of 2 weeks you will begin to notice some gradual improvement of your technique and stamina.
If you want to improve your pedal technique, then 15 minutes of daily playing of scales and arpeggios with your feet will do the trick.
Of course, keep in mind that your practice in developing your organ technique should be wise, meaning that every detail should be correct: notes, rhythms, tempo, fingering, pedaling, articulation (perfect legato whenever possible), hand and feet position, pulse among other things. It is dangerous to try to play faster before you are ready for it.
Please note that this advice is only for people who absolutely can't find more than 60 minutes of time for organ practice. On the other hand, if you have more time available in your day, devoting up to 1 hour for technical studies would be much more beneficial for your development as an organist in general.
By the way, do you want to learn my special powerful techniques which help me to master any piece of organ music up to 10 times faster? If so, download my video Organ Practice Guide.