how long does it take?
Well, let's see.
If you were smoking for a few years, your brain gets accustom to the endorfins being activated by the smoke, and it takes 8 to 12 months to properly get those brain functions to work without that cigarette smoke, so how long does it take to change behavior from karate to Aikido?
It takes as long as it takes.
No, really, not trying to be funny ...
The overanxiousness of coming from another martial art takes time to acquire skills of another art.
In karate, you should have been taking notes, reviewing techniques, and keeping track of what you learned in each class, if not .. then you were being spoon fed. Sometimes a teacher will do that, review for upcoming tests, and even go through a test for a student at the end of a class to smooth out the rough edges, but you either have to ask for it, or ask some of your classmates to help you ... that is part of the learning social process of Aikido.
I cannot help but smile at the progress many of the students have made in two years. From stumbling, bumbling, ineptitude, they have become proficient enough to help the teacher in most demonstations, and even help with the childrens class as assistents to the teacher. That is quite a long distance from the stumbling of the first six months when they first came to Aikido.
Don't be in too much of hurry to be a master practitioner. There are a lot of bad habits from Karate that will haunt you for many years, but when you learn to blend them into your Aikido practice, the clarity of what you have learned will astound you.
As far as learning the techniques, their names, and what they do ... print out the Aikido throws here on the Aikiweb, then add your own notes to what they are, and stick it up near your computer, and anywhere else you think it will be read to imprint the words into the mind.
I am pretty thick when it comes to words, even though transition and the "advanced techniques" come quite easier than the words that describe them. Besides, many of them are still in my head as judo, jujitsu, and part of my karate training, so I do understand part of your dilemma.
Remember, a black belt never protected anyone in a real fight situation, but knowledge always does.
Train for the knowledge, and the grade or kyu will come in its own time.