Cryptocurrencies use fees (transaction fees or miner fees) to pay miners for confirming the transactions that are requested on the blockchain. The amount of fee varies from currency to currency. BC Vault application will suggest you a fee that should put your transaction through in 1-2 blocks, but you can always manually adjust the fee should you wish so.
The higher fee you pay, the faster your transaction will be confirmed by the miners.
So if we take an example with Bitcoin (BTC) that has block time of 10min the recommended fee should generally provide you with a transaction confirmation from anywhere between 5-20min.
You might catch next block very quickly from your transaction or in worst case in 10 minutes (as you have to wait for at least next block).
In Ethereum (ETH) for example, block times are much faster 10-19s.
When networks become extremely busy it might happen that you will have to wait hours or even days for transaction confirmation.
This is an example of how Ethereum Gas Price (Fees) changes over time, you can see quite some deviation when the network is really busy:
Check this article for more detailed information about fees: Miner fees