How long should I meditate every day to be considered beneficial and effective? How fast can I see the results of meditation? What noticeable change can I experience if I meditate regularly?

As little as a minute of meditation can make a difference. I use some guided meditation because my ADD brain just bounces around. I started out by doing a minute and every week I added another minute. What changes you can see are going to very. I noticed how much calmer I am with my kid.

I think 10 minutes a day are the minimum and then you can add how much you want. To see the results you need to wait weeks. Once learned the tecnique you will be able to controll your breath in hard moments, resultin in a better control of your mind

There is no minimum time to have benefit from meditation. More importantly is to give yourself the length of experience you are comfortable with and not be hard on yourself. It can feel a bit challenging, so be compassionate with yourself if you get lost in everyday thoughts. It is ok. How fast you see the changes in your life is relative, but I would say that the more you give yourself entirely to feel the sensations and emotions along the meditation process, the better you will recognize body and mind sensations in your every day life.
For example, I start to recognize how I am feeling earlier than before; I start to understand that if I am sad, it is in my control to create a different stimulus, one that makes me feel good and that it can help to take control again; sometimes I have a bigger perception on the feeling of water in the shower, or of a smell outside, or the floor under my shoes.