Maybe you're doing a simple Google search and the results are being customized to you.
1. If you're using Google Chrome, try the search in an "Incognito" window, to see a more generic result.
2. If you're searching from different computers, the results will be personalized to the history and location of those computers... a laptop can also expect different results at different IP addresses.
3. Maybe Google's resources are limited, and processing is different based upon demand. The results might become different if personalization or testing resources are limited. (Google is constantly running tests, which cause changes in their results) In your case, the U.S. waking up and doing searches might decrease the resources which are used to customize your results or test variants upon you.
4. Maybe your ISP or employer is caching, and you're seeing the results which someone else generated. This seems unlikely.