Salam alaykum,
I have an IBKR account, cash account.
When I convert currency, Currency conversion is done through a spot forex trade, and forex trades settle in T+2 business days.
You will see the converted currency balances immediately after execution but the actual trade settlement will take its due time
it is similar to stock trade settlement, you submit an order, it gets executed at a certain price, then it settle in T+2 business day
But I can buy a stock immediately with my cash account because the settlement date of a stock is similar (2 days).
This conversion of devise halal or haram thanks.