What should I do when I feel lustful while washing the penis during istinja (cleaning oneself after urinating) or when bathing, which delays the ghusl (ritual bath) for an hour?

If touching is limited to what is necessary, such as removing impurity, then there is no harm in the ensuing arousal, provided that one does not intentionally incite lust leading to forbidden masturbation. If the arousal results in the emission of manī (seminal fluid), a full ghusl (definition) (ritual bath) is obligatory. If it is madhī (pre-seminal fluid), only washing the penis is obligatory. One should not prolong the washing time beyond necessity to avoid waswasa (whispers/obsessive thoughts).