Is it permissible for a person suffering from Irritable Bowel Syndrome (IBS) to perform ablution before the time for the Asr prayer begins, in order to perform the prayer, knowing that she leaves the house before the prayer time and fears missing it?

A person afflicted with urinary incontinence or constant flatulence must purify himself and perform ablution for the time of each prayer, then pray immediately. What exits from him during prayer does not harm him. As for performing ablution before the prayer time enters, it is not valid for prayer after the time has entered, unless nothing exits from him.