It depends really. Transactions are usually processed based on the fee associated with them. If the network is exceptionally busy and you send a transaction with a low fee, yeah it'll take a while, but when creating the transaction you can adjust the fee (and most wallets will give you a few options) to make your transaction more valuable to miners, so it will be picked up more quickly.

Bitcoin from wallet A to wallet B usually only takes about 20 minutes but fiat -> bitcoin and bitcoin -> fiat can take a while, typically a day or so each and more if backlogged.