There is no set, predictable pattern.
Yes, some attain gradually. Don't worry about gradualism too much though, just figure out how to Practice better and better, keep improving your Dharma knowledge. Your recognition that your mind is racing is the 1st step. (Most ordinary people are at step 0. They don't even know that their mind is hell.)
Yes, there are many cases of sudden enlightenment, and such people always had great amount of merit and past life cultivation and already had tremendous concentration power (2nd Training).
Read a Buddhist book. I suggest reading the articles here. Read Mastering the Core Teachings of the Buddha for the best hardcore introduction to Buddhism ever. It's free.
It's not as simple as force yourself to sit for 20 minutes twice a day and get enlightened...there is a lot to the whole Buddhist work and it is plain out stupid for someone to expect realization and get it. Realization is a type of non-attainment. Read the Diamond Sutra and Heart Sutra to start to understand this concept.
Also, unless you can focus your mind (the 2nd training) so well that you are absolutely clear and blissful (this happiness is happier than a constant orgasm, jhana) the 3rd training (which involves "realization") is far far off.
Learn to concentrate first (2nd training).
You also have to learn how to meditate correctly or else you can meditate for 24/7 for 100 years and nothing will happen - no stilling of the mind, nothing, just racy mind getting worse and worse until you give up.
"Don't have hope for Enlightenment but Practice all your life." --Milarepa