First of all, we have to understand what practice is. An old saying teaches that a practice is like a boiling water - without heat it cools down. In other words, you have to constantly add some effort which facilitates the progress in whatever it is you are trying to excel.
In the case of organ practice, you have to practice regularly. Your organ piece will become much better over time if you practice regularly and wisely.
Now let's return to the question if you have several pieces to prepare. Many people practice sporadically and without a system. In other words, they just play the pieces on their list from the beginning until the end.
However, they are never sure if they will prepare them by the due date. This type of practice will not lead you very far in organ playing.
Let's pretend you have 2 hours a day set aside for practicing. I recommend you approach practicing systematically and methodically in one of the following ways:
1. Treat all the pieces on your list as one long piece. In one practice session, learn several lines or a page for 2 hours in a slow tempo. Then the next day repeat the previously learned material and learn several new lines of music. It is best if you learn one short fragment (up to 1 line of music) at a time.
This way you will eventually approach the last page of the last composition on your list while practicing for 2 hours daily. Remember to reinforce the pieces that you have mastered so far regularly. If learning new music would require you to repeat a certain passage up to 10 times, it is enough to repeat the previously mastered music 3 times.
2. Practice several pieces every day for 2 hours. With this approach, you will have to alternate the pieces on your list every other day. For example, take one half of your program and practice it on Monday, Wednesday, and Friday. Then take another half of your program and practice it on Tuesday, Thursday, and Saturday.
Again, when learning new organ music, repeat each fragment 10 times slowly in separate parts, combinations of 2 voices, 3 voices, and finally all parts together. When you repeat the music that you already know, repeat all parts together 3 times in a slow tempo.
Whether you choose the first or the second approach, for best results, make sure your fingering, pedaling, notes, rhythms, articulation, and ornamentation are correct in each repetition. Do not forget to take a break every 30 minutes or so, stretch and relax for 5-10 minutes.
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 free Organ Practice Guide.
Or if you really want to learn to play any organ composition at sight fluently and without mistakes while working only 15 minutes a day, check out my systematic master course in Organ Sight-Reading.