Ref. No. 1142/42-372
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
The white substance maybe discharged when you were sleeping in before Asr. You have to repeat the Asr and Maghrib after taking a compulsory bath. Due to only thoughts of wet dream, Ghusl is not obligatory on you until you see semen discharge. The discharge you feel due to lust without visible semen is called ‘Mazi’. Due to Mazi, only wadhu is broken not Ghusl.
And Allah knows best
Darul Uloom Waqf Deoband