Is it permissible for a person afflicted with urinary incontinence, who cannot determine the duration of urine cessation after urinating, to perform istinja (cleansing), cover the affected area, and pray with the congregation, knowing that the drops might stop before the end of the prayer time? And is it obligatory for him to repeat istinja if he performed istinja and covered the area more than an hour before the prayer, and then the prayer time commenced?

If you find a time during the prayer where no urine exits, you must wait until that time to pray with a valid purification. In this case, congregational prayer is not obligatory for you, because praying with a valid purification takes precedence over performing congregational prayer. If the urine ceases after relieving oneself for a known duration, then one should relieve oneself before the prayer time enters by this duration, then take precautions with a tissue or similar to avoid soiling clothes, then perform istinja’ and wudu’ to catch the congregational prayer.