What is the ruling on sitting at a computer for three hours a day?

The computer is a machine of great benefit, and its use is originally permissible. However, it may acquire one of the legal rulings (obligatory, recommended, disliked, forbidden) depending on its use. Thus, it becomes obligatory if it is the only means to an obligation, recommended if it is used for a recommended act, forbidden if used for a forbidden act, and disliked if it leads to wasting time.

Secondly: Persistence in something affects its legal ruling. What is permissible may become disliked or forbidden through persistence, and what is disliked may become forbidden. So, permissible amusement with the computer, if the user persists in it, may exit the realm of permissibility to dislikeness or prohibition, because it is a waste of time in what does not benefit in this life or the Hereafter, and it is blameworthy even if it is permissible.