All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Performing Ghusl (ritual bath) while Maniyy (semen) is still coming out is not valid and does not remove the state of ritual impurity. Ghusl should rather be performed after the discharge ceases.
There is no specific period after which the discharge should cease because people are different in this regard. Whenever you know that the Maniyy has stopped to come out, you should perform Ghusl then. But if you happened to discharge Maniyy again after performing Ghusl, do you have to repeat the Ghusl or not? Scholars held different opinions regarding this case. The majority held that it is not obligatory to repeat the Ghusl and that ablution would be sufficient in this regard, and this is the opinion we adopt at Islamweb. The Shaafi‘i scholars, on the other hand, held that repeating Ghusl is obligatory in such a case.
Allah Knows best.