Transactions can be done instantly, yes. Like a credit card, when you make a Bitcoin transaction, you send it to the entire Bitcoin network. So, in a few seconds, all other Bitcoin nodes will receive it. However, the fact that different nodes get the message does not guarantee that the transaction is permanent.
As there are many transactions in progress in Bitcoin Blockchain, the number of transactions pending verification is high. Miners must include the transactions in the next block. The blocks constitute the blockchain, and a new block is added every 10 minutes (this is the theoretical average time, the real average being 8 to 9 minutes). Whenever your transaction is included in a block, you can be almost sure that it will be permanent, but it is always possible that the block is orphaned. Once an additional block has been added to the block with your transaction, the chances of being an orphan are negligible.
You can think of blocks as settlements in the traditional world. While it’s not the same, it is comparable. When you buy a coffee with your credit card, it takes up to 90 days for the settlement to occur. In the Bitcoin world, this settlement is achieved in hours, based on the block the transaction will get in. Just as in the credit cards world, in the Bitcoin world, you can also defer a settlement for later. For example, you could pay a coffee on the Lightning Network, and the settlement of all coffee transactions can happen on a predefined timescale.
Initially, the Bitcoin community had suggested that six blocks or confirmations would be the perfect time to consider an irreversible transaction. It takes an hour on average to obtain the six confirmations, which makes this settlement network far superior to any existing system. Most valid transactions, certainly those with transaction fees, will be included in a block without any problems. Besides, millions of transactions can be made continuously over the Lightning Network, a second layer above Bitcoin, benefiting from the security of the main chain.