Is it permissible to read the entire Qur’an in one day, bearing in mind that some say it is not permissible to read it in less than three days?

Reading the Quran is a great act of worship. The Prophet (peace be upon him) encouraged its recitation and completion within seven days, and he forbade its completion in less than three days for those who made it a habit, as it leads to a lack of understanding of the Quran and the neglect of other obligations. However, there is no harm in completing it in less than three days occasionally, such as for reviewing memorization, or utilizing a blessed time like Ramadan (definition), or a blessed place like Mecca, or a special circumstance like I'tikaf (spiritual retreat).