We are confused by the statements of the imams regarding the definition of the recommended and desirable i'tikaf. They said that the recommended i'tikaf is in the last ten days of Ramadan, and the desirable i'tikaf is outside of the last ten days of Ramadan, meaning in the beginning of Ramadan, in the middle, or outside of Ramadan. Does this mean that the duration of the last ten days of Ramadan is a criterion rather than a condition, such that one cannot perform the desirable i'tikaf during this time, and that anyone who wants to perform the recommended i'tikaf must complete the entire duration of the last ten days, otherwise it is not considered recommended?