I will be preparing a dinner which includes chicken which will be stuffed with different types of cheese, tomatoes and spinach but before that I have to marinate the chicken. In one of the recipes it was asked to marinate the chicken for 2 hours, but the chicken I bought is pretty thick. So how long should I marinate it?
Marination is generally a surface treatment, so the thickness of your chicken is irrelevant. Really, the only thing that can penetrate is salt, primarily because of molecule size. You can read a good explanation here. I would say you're good with the 2 hours, but as you will see when you read the article, you might not even need that long...or you might want to rethink the marinade altogether.
Marinades can be made with a many ingredients with dissimilar flavors and touches. Those unfamiliar with the procedure of marinating chicken should know that marinating can be a 2 minute, 2-hour, or 2-day procedure, depending on what you wish to achieve. So before getting stared you should plan which ingredients you will use and how you want to marinate the chicken, which flavor you like etc. Compared to other meats, a chicken needs a comparatively less time for marinating than lamb, beef, or pork. A usual roast takes 4-6 hours, while steaks and fillets need about a 4-hour marinating time for a very tender, flavorful cut.
I found a very informative article about "how long to marinate chicken" over online. I guess you will like that too.