When you transfer cryptocurrency, it will leave your cryptocurrency wallet instantly, but will only arrive once the transaction has been validated in the transaction ledger (blockchain).
You can read more information about it in "How long does it take for crypytocurrency deposit transaction to be processed?”.
Potential reasons for a long transaction processing time:
- The transaction fee was too low. This often happens if you send a small amount, as transaction fees are often set as a percentage of the amount you send;
- The same cryptocurrency was sent by mistake. Such a transaction will not be validated;
- The cryptocurrency is not validated. You are sending cryptocurrency that has not yet been sent to your wallet (the one it is sent from), and therefore it will only be sent after confirmation;
- There is a high volume of transactions going through the network, so you will need a higher transaction fee to send it in the normal time frame.