Ideally, search results should be loaded immediately. However, it's not always possible, and your job is to indicate the search progress and inform users of how long it may take. A good product should notify users about what's going on in the system and provide feedback on users' actions within a reasonable time.

Use progress bars for this purpose when a page doesn't contain a lot of information and loading doesn't take more than 300ms. Show a progress bar or spinner and offer a short but informative explanation of the situation.

If the loading takes time, use a skeleton loader, and add an animation accompanied by witty and helpful microcopy to make the waiting less boring and encourage users to stay patient.