This is really frustrating. Many of them even can't wait that long and quit practicing long before they start to see the results of their labors.
We all want to be able to sight-read organ compositions well, without mistakes, fluently, seemingly effortless. Bach was said to have such ability at his time. Imagine if you only developed one tenth of his skills, would it still be worth it?
I think it would. So how about trying out 50 day organ sight-reading challenge? Here is what you do:
Play at a slow practice tempo one piece from Bach's Orgelbüchlein every day for 50 days from the beginning until the end without stopping.
Since there are 46 chorale preludes in this collection and some of them have more than one verse, it would take almost 50 days to complete the challenge.
Start today - the pieces are only one or two pages long - it takes only 5-10 minutes to complete every day's assignment (and yes, you can practice during TV commercials if you don't have much time available in your day).
By the way, do you want to master sight-reading on the organ? If so, check out my Organ Sight-Reading Master Course.