Credit card money movement comes in two phases, authorization and capture.
In the authorization phase, the merchant requests the bank to "hold" on your account for a certain amount. This checks to ensure that you have the funds necessary to complete the purchase. The amount is usually the exact amount of the purchase, but sometimes it can be higher, e.g. when you stop to purchase gasoline and don't know how much it will cost to fill up, the service station might authorize your card for $100.
Authorization will show up in your bank's credit card processing system immediately, but may not show up in the core banking system or the online banking web site for some time afterward, depending on how old their systems are and how they'd decided to connect their computers together. Also, merchants are not required to perform a separate authorization, and if they do, they might not do it immediately; so just because you don't see a transaction yet doesn't mean one isn't coming. When it does show up, it'll affect your available balance, but not your card's ledger balance or main balance, and the transaction may or may not appear online, with or without a date, or as a memo post.
The second phase-- capture-- typically occurs when the order ships. At this point a second request is sent to the bank to move the money. The transaction may remain in a memo posted state for the remainder of the day, or it might not; it will almost always hard post by the opening of business the next day, and should appear online the same morning. Any holds on your account would be removed simultaneously, and in the end you'll see a single transaction in your online banking history for the purchase amount. That being said, the merchant may not be under an obligation to charge your card immediately, so it may take an indeterminate of time for the transaction to appear, especially with smaller merchants.
If you are concerned about an incidental charge, you should contact your bank for the most up-to-date information. It is often the case that a customer service representative has access to systems that contain better information than the online banking system, and can tell you whether an authorization or capture has occurred recently. If the transaction has not shown up yet, they can put a block on the card for you, or block the specific merchant or the merchant's country.