How can one calculate the times for the departure of the Dhuhr, Asr, and Maghrib prayers, in order to combine them with the prayer that follows, due to urinary incontinence?

The Dhuhr time ends when the shadow of everything becomes like its own length, excluding the shadow at zenith. The Asr time begins when the Dhuhr time ends and continues until the shadow of everything becomes twice its own length, excluding the shadow at zenith. Its time extends to sunset when necessary. As for the Maghrib time, it is from the disappearance of the sun's disc until the disappearance of the red twilight.