Deposits are credited only after a minimum of two block confirmations. The average block time for the bitcoin blockchain is ~10 mins. Thus, it may take around 20 mins from transaction initiation for your deposit to show up in your Delta Exchange wallet.
Please also ensure that you send only Bitcoin to your Delta Exchange deposit address. Litecoin, Bitcoin Cash and Tether networks accept Bitcoin addresses as valid. If you send any unsupported coins, they will be lost and we won’t be able to recover them.