بسم الله الرحمن الرحيم
(Fatwa: 89/62/SN=2/1439)
For ghusl of janabat (impurity) the obligatory acts are: gargling well, sending water in the nose and pouring water over the whole body. These acts may be carried out within fifteen minutes, even in less than it. Thus you should try to wind up your ghusl within ten to fifteen minutes. Yet, if you have some doubt and waswasah then you must not pay any attention towards it. If you do ghusl in this way for some days then in-shaAllah you won’t be affected by waswasah.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband